I’m sorry but without more knowledge (and ideally, access to) about that printer, I can’t really help you adapt it because I’m not entirely sure how the driver is, works, gets installed…
All I can do is suggesting you look, if possible, into where it installs the files and see if you can manually put them somewhere under /var or /opt (which you can write into). Then, once placed in a specific place, you’ll probably have to search for a .PPD file in the installed location and modify it with a text editor in case it points out internally to the paths the driver was meant to be installed into.
Sorry not to be more precise but, as you can imagine, there are way too many variables and I can’t really advise you more closely on this particular case. I hope this is helpful in any case, though.
PS: To be clear, I no longer work at Endless. I do this entirely on my spare time, which is once again why I can’t really devote more time/energy than this in the forum, sorry.