Ultimately this comes down to changing the versioning string for "Hometown version 1.0.8, synchronized with Mastodon 3.5.5" from

1.0.8+3.5.5

to

3.5.5+hometown-1.0.8

I still cringe a little to look at it but I understand that it'll help other projects and I really want as much 3rd party Hometown support as possible.

As usual: please don't ask why I have decided to do it this way or propose alternatives until you have read the Github thread which contains the rationale.