Since CA1 is still closed about halfway between Morro Bay and Big Sur, you will need to take US101, unless you wish to negotiate an tortuous, narrow road over the Coast Range by Ft. Hunter Liggett to reach 101 around San Miguel. I have not driven this particular road, but I understand that it takes well over an hour to go between SR1 and US101.
There is another back road from Carmel Valley to Greenfield.
Regardless, there is a Supercharger in Atascadero, so as long as you have ample charge upon departure from Monterey, you should be able to stop in Atascadero for 20-30 minutes to grab enough charge for Buellton.