According to http://docs.oracle.com/javafx/2/deployment/preloaders.htm (section "9.2 Packaging an Application with a Preloader") when we're packaging with preloader we must set
JavaFX-Preloader-Class: <package>.<classname> in MANIFEST of the created jar, then in jnlp file we have to see jfx:javafx-desc tag with argument preloader-class="<package>.<classname>".
Let's try to do it: we see that there's no difference with this option

Attach some helloworld project which you can build with this option by:
ant -f simple-build-big.xml deploy-with-application