I had a similar issue. You actually do not need to register in CA if it's only temporary. They say after 30 days of living there you do, but honestly you don't. As long as your current state plates and tags are current, and you're insured you're fine. This was actually told to me by a friend at the CA DMV. The only issue would be if you kept getting stopped by the same cop, which is very unlikely. I spend half my year in Oregon and half in CA, and I've never had a problem. It it's a PIA to register a car with an out of state title, especially if there is a lone still on the car. Lots of paperwork, and unnecessary. If it's only for a few months I'd not worry about it.
2009 E93 335i | Jet | Black Dakota | Grey Poplar | ZPP | ZSP | ZCW | Step | Paddles | i-Drive | CA | Sirius | HD | Logic7 | 06FL | 06NF | PDC | OEM Alarm | LUX
Retired: 2007 E92 335i
Retired: 2006 E90 330i