I just had a peek at the source code of the plug-in. It's basically already setup to add another service like Lemmy, as it supports Nebula and one other service with the same codebase.

I think it would almost trivial to add Lemmy. I may look into doing it if i get bored and have the time, but not sure when that would be. Have you contacted the git maintainer for that plug-in and asked him to add Lemmy support? He could do it much quicker since he's already familiar with the code and from what I saw, it would be about 30-60 minutes worth of work for someone familiar with the codebase already. I may be grossly underestimating that since I did not do an in depth dive, but from what I can tell it would be pretty simple.

What I would do is:

Add a new variable that lets you configure what Lemmy instance you want to point to
Copy the objects from reddit to a new lemmy object.
Adjust the URL and /r/ to /c/

Might have to fiddle with the User view code a bit

But other than that, everything else code wise should be a drop in replacement from what I can tell.