It turns out, that despite the name of this thread, the problem is not a source requirement; it is the autobuilder. It would be wonderful to have a program like PyPackager that would make complete packages that are able to be fed to the autobuilder, even though they don't need compiling. That is, the autobuilder will simply take the package and build the deb without attempting to compile anything.
But this is a cheat, and mainly why I decided to go to the non-free repository. The whole point of a free repository with source code that is guarded by an autobuilder is that the packages can be rebuilt for new versions of the OS. If you cheat the system and upload packages like mine (with binary bits), it defeats the purpose.
Bundyo's hostwin app, written in Vala, is another tricky bit.