Please add the ability to load custom BCProcessor class.
Loading by checking System.getProperty() would be okay.

Code sample:

    protected boolean prepareCheck(MultipleFileReader in, PrintWriter log) {
        if (isValueTracked == null) {
            isValueTracked = Boolean.TRUE;
        }

        if (EXT_MODE.equals(mode)) {
            Modifier.VOLATILE.setTracked(true);
        } else {
            Modifier.VOLATILE.setTracked(false);
        }

        if (mode == null) {
            mode = SOURCE_MODE;
        }
        MemberType.setMode(BINARY_MODE.equals(mode));

        isOneWayConstantChecking = isValueTracked.booleanValue() && BINARY_MODE.equals(mode) || !isStatic;

        if (SOURCE_MODE.equals(mode) || EXT_MODE.equals(mode)) {
            isThrowsRemoved = false;
        }

        if (BINARY_MODE.equals(mode)) {
            isThrowsRemoved = true;
        }
        MemberType.setMode(BINARY_MODE.equals(mode));

        if (isValueTracked.booleanValue() && !in.isFeatureSupported(FeaturesHolder.ConstInfo)) {
            String errmsg = i18nSt.getString("SignatureTest.mesg.sigfile.noconst");
            log.println(errmsg);
            return failed(errmsg);
        }
        // If sigfile doesn't contain constant values, constant checking
        // is impossible
        if (!in.isFeatureSupported(FeaturesHolder.ConstInfo)) {
            isValueTracked = Boolean.FALSE;
        }

        setConstantValuesTracked(isValueTracked.booleanValue());
FieldDescr.setConstantValuesTracked(isConstantValuesTracked());
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.report"));
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.basevers", in.getApiVersion()));
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.testvers", apiVersion));

        if (!isThrowsRemoved) {
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.checkmode.norm", mode));
        } else {
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.checkmode.removed", mode));
        }

        if (isValueTracked.booleanValue()) {
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.constcheck", i18nSt.getString("SignatureTest.mesg.sigtest.constcheck.on")));
        } else {
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.constcheck", i18nSt.getString("SignatureTest.mesg.sigtest.constcheck.off")));
        }

        if (!isTigerFeaturesTracked) {
log.println(i18nSt.getString("SignatureTest.mesg.sigtest.tigercheck"));
        }

        log.println();

        classpath.printErrors(log);

        trackedClassNames = new HashSet();

        ClassDescriptionLoader loader = getClassDescrLoader();
        setupLoaders(loader, in);
        loader = getClassDescrLoader();

        if (!isValueTracked.booleanValue() && loader instanceof LoadingHints) {
            ((LoadingHints) loader).addLoadingHint(LoadingHints.DONT_READ_VALUES);
        }

        testableHierarchy = new ClassHierarchyImpl(loader, trackMode);

        testableMCBuilder = new MemberCollectionBuilder(this, "source:testable");

        signatureClassesHierarchy = new ClassHierarchyImpl(in, trackMode);

        String bcProcClassName = System.getProperty("BC_PROC_CLASS");
        Class bcProcClass = BCProcessor.class;
        if (bcProcClassName != null) {
            bcProcClass = Class.forName(bcProcClassName);
        }


        // creates ErrorFormatter.
        if ((outFormat != null) && FORMAT_PLAIN.equals(outFormat)) {
            setErrorManager(new ErrorFormatter(log));
        } else if ((outFormat != null) && FORMAT_HUMAN.equals(outFormat)) {
            setErrorManager(new HumanErrorFormatter(log, isVerbose,
                    reportWarningAsError ? Level.WARNING : Level.SEVERE));
        } else if ((outFormat != null) && FORMAT_BACKWARD.equals(outFormat)) {


            try {

                Class[] argTypes = {PrintWriter.class, Boolean.class, Boolean.class,
                        ClassHierarchy.class, ClassHierarchy.class, Level.class, Boolean.class};

                Object[] args = {log, isVerbose, BINARY_MODE.equals(mode),
                        testableHierarchy, signatureClassesHierarchy,
                        reportWarningAsError ? Level.WARNING : Level.SEVERE, extensibleInterfaces};

                Constructor c = bcProcClass.getConstructor(argTypes);
                ErrorFormatter ef = (ErrorFormatter) c.newInstance(args);
                setErrorManager(ef);

            } catch (NoSuchMethodException ex) {
                ex.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }


        } else {
            setErrorManager(new SortedErrorFormatter(log, isVerbose));
        }

        return true;
    }