hi,
Yes, I did renew my California driver's license from the UK. I wrote a letter to the DMV in Sacramento, and they responded that I could only renew 60 days in advance. So I sent another letter exactly 60 days in advance of the expiration date. They sent me the forms, I filled them out and paid the fee by cheque, and sent it all in. I heard nothing for quite a while and called them up. They assured me they were working on it, and I did eventually get the renewal in the mail, but it arrived a week after the expiration date.
You can find information online about the process in the California DMV site.