If engine manufacturers are complaining about not getting enough exposure, why not regulate it that during all testing (not race weekends), the cars must run 'testing' liveries representing the engine manufacturer primarily, and also the chassis constructor?
The Red Bull, for instance, would be yellow instead of blue, the bull logo on the airbox would be black and the red bull lettering on the front wings would be in black and white instead. I don't know how Infinity would fit into it (that's already renault-nissan politics' problem, so I'll leave it to them).
EDIT: something like this (it's hard to make dark blue into gloss yellow, so just pretend or something)
This way, during testing, Renault would have 6 (?) yellow cars on track - GREAT for them, Ferrari would have a bunch of red cars, and Mercedes would have a gaggle of silver cars. It'd also have the added bonus of being able to show the cars off during testing, and still have them looking new and possibly surprising when they turn up for round one in their proper colours.