When I acquired my 7900 with bad green channel I looked into ways to still use it for color. Turns out it's as simple as using the 7890 driver. But one of the things I initially tried was modifying the Gutenprint driver for the printer. It was a fairly simple process as each printer has a configuration page where the inks are described. You could try this and omit the LM ink from the mix. Obviously you would need to make custom profiles, and your gamut will be reduced. Personally I would convert the printer to black and white, either through Piezography or just using QTR if you expect the printer to further die.
Just out of curiosity, do you have the auto nozzle check feature still on? I suspect that's what killed my 7900 (before I acquired it).