Shorthand for including an output file of a genrule directory as a src

If you have a genrule that creates a directory with several files, it's a bit of a pain to write another genrule rule for each (expected) output, just to be able to pass it to *_library (java, python, etc). It would be nice to allow you to somehow specify this in the sources - maybe via flavors (although it is a bit hackish)? e.g.

genrule(
    name='gen_my_thing',
    out='things',
    cmd='$(exe :my_custom_generator) $SRCDIR $OUT',
    srcs=glob(['File1.java', 'File2.java']),
)

java_library(
    name='lib',
    srcs=[
        ':gen_my_thing#lib_output/File1Out.java',
        ':gen_my_thing#lib_output/File2Out.java',
    ]
)