I think that probably this will be attempted at some point by someone in the open source community. There are other apps that already work this way for other services.
But from the little I’ve read, I get the impression that the Infinity for Reddit developer feels that he cannot (officially) do this based on what Reddit communicated to him. He has been careful with his words (not encouraging or directly helping people to use their own key and not making an official guide or anything, while at the same time making it clear that it is possible and hinting at it).
I think you are right, and I think that an automated script might be the best approach to thread the needle and avoid a crackdown while still making it easy enough to implement.
I imagine like with youtube frontends, we will see a diversity of projects and approaches emerge to address this problem.