Since 0.4.1 JTransc allows adding custom targets. All you have to do is to add to the classpath a ServiceLoader enabled service at file:
META-INF/services/com.jtransc.gen.GenTargetDescriptor
And implement your own GenTargetDescriptor
so JTransc can use your target.
Since 0.4.x JTransc metaprogramming plugins enable reflection + ServiceLoader for free without implementing yourself in your target.