Would it be possible that the push interface can use target systems from what is maintained in Special:Interwiki? If not so, maybe something like Special:Interwiki could be used as template in how to maintain target systems within MediaWiki, meaning system data can be maintained without changing the LocalSettings file.
Topic on Extension talk:Push
I don't think using the interwiki links for this is a good idea, as you'll end up with some 20-ish push targets on most wikis, while you probably only care about one or a few. An interface to manage targets would be neat, but is not needed by my employer at this point.