If you have exhausted all appeals with the FTB, then your next appeal would be to the California Board of Equalization (BOE). If that appeal fails, then you would have to pay the tax due, and then file an appeal with the California Superior Court. For a discussion of BOE appeals, see this link.
If your employer is located in California, you could subpoena the employer's custodian of records (fancy name for person who is legally required to do the employer's record archiving) to appear and testify to what it knows about your place of residence during the 2008 tax year. And, you could force the custodian to bring all of your various paperwork with contact info, showing that you were residing in Pennsylvania during that time period. If the employer is in PA, then you could probably get the records via subpoena, but not the personal appearance and testimony of the custodian.
Alternatively, you could sue the employer for fraud
, on grounds that the employer's misrepresentation on the W-2 has induced actual reliance by the FTB and by you, and you have been damaged as a consequence. Your damages would be whatever you owe the FTB. However, you would not be entitled to attorney's fees, so this could be a bit of a losing money proposition -- though a nasty letter from a lawyer threatening to sue, may get the employer to adjust its form, given that the employer also would have to pay it's own attorney's fees (and, for a fraud claim, I could see $10-15,000 burned by each side in litigating the issue. Probably not worth fighting over, so that letter could move the mountain and get you the W-2c.
For a civil litigation attorney referral, see this link
Hope this helps.