DMV can wipe fees away with the click of a button. I have done it many, many, many times. You can register a vehicle in another state, and re register in california, with zero fees, and they dont care about the other state plates. I just did it, and am smogging a washington truck today in california. It was even 5 yrs out of reg in washington, and still 0 california fees besides current year and a weigh in. I only have to pass the emissions the truck was designed to pass either, not calis.
If you want to wipe back fees, dress nice, clean clothes, clean shaven. Have a good story about how either vehicle came from family, or how you can prove its sat idle and not on state roads for the entire duration. Have cash ready for the current years fees.
Also, if you have back fees on a rig, go in, and try to non op it. In my town, everytime I have non opped something, they wiped any back fees, I just told them I bought it for project. Once its non opped, its easy to take it, off, but either go to a dif dmv or wait a week or two.