jasm tool should support the values:
this_class (#ID | IDENT); // CLASSNAME
super_class (#ID | IDENT); // SUPERCLASSNAME

Then the command `java -jar asmtools.jar jasm -d . FILE.jasm` where the jasm file is as follows:
class FILENAME.data {
  this_class[:] CLASSNAME;
  super_class[:] SUPERCLASSNAME;
}
will produce a binary file `FILENAME.data` which, after decompiling (`java -jar asmtools.jar jdis FILENAME.data`), will be:

super class CLASSNAME extends SUPERCLASSNAME version 45:0 {}