PG&E has a number of rate schedules, one being the E9A when you own an electric vehicle, which has fairly low rates during the midnight to 7am period. You can check your current rate schedule at http://www.pge.com/tariffs/ERS.SHTML#ERS and see if the E9A might be better for you. Lots of tiered times. It does not change your baseline.
There is also a E9B option, if you have a separate meter to your MS charger that has the advantage of a second baseline, but it requires a second meter and wiring. It will only be around for about 20 months, so it would need to save quite a bit to pay back the costs of the second meter and wiring in a short time.
If you do want to switch, rather than go through long waits and many transfers (as I just did), call the Building and Renovation dept at 1-877-743-7782. You do have to have a smart meter and have taken delivery of your MS, but other than that, it's easy to switch.
E9 is going away soon (April?), and it will be replaced with a newer EV rate plan, but you can keep the E9 until the end of 2014. I don't know if this will be better or not, but my guess is E9 will be cheaper and if not, you should be able to switch to EV when it is available.