If it's going to be a really cold night and the trees have a lot of tender growth you can hang incandescent Christmas tree lights and then cover the tree.  If it's dormant a light frost wont hurt it. 

Christmas lights wouldn't work for my in-ground trees since they will be scattered over a few acres. However, I really like that idea for trees close to the house, or even around my potted tees, with a plastic pup-tent over them.

I don't know that you're going to find incandescent Xmas lights in California.

Hi cyberfarmer,
I would try to let the trees go to dormancy and wouldn't try to avoid the dormancy step - but perhaps your climate does not allow for dormancy ?
Last year I had a fruiting plant that I wanted to protect (The plant was in the small greenhouse and I wanted to start the tomatoes ),
and I put 4 stakes with a clear plastic bag over the 4 stakes and falling to the dirt and secured all around the stakes to the dirt.
My plant was not a fig tree.
For me the worst is the cold falling from the upper side, so a roof made of plastic with walls falling on the sides should do the job.
Here, my plant was half shaded - In full sun, you might want to poke some holes for not cooking the tree on sunny days.
You just need to check every now and then, especially in rainy days as a reservoir might appear on the top of the four stakes, and you need to empty it to keep the plastic from being split .
Now of course if your trees are XXXL size ... I would consider some pruning ...

Paul,

I'm not sure I understand the issue.  Is the problem that you have multiple frost/warm period cycles where the trees keep trying to push new growth that gets killed by frosts?  Are you concerned that process is hurting the overall health of your trees? 

If so, perhaps you could wrap them on the chilly nights and use the heated rock technique.  If you put a large rock in a pot and boil the water it will absorb a lot of heat that it will give off slowly.  So put the rock inside the wrap next to the tree.  Probably enough to make it through the night.  Just an idea, I have no practical experience with this.

Other thing would be to use lights attached to some sort of battery, but that could get expensive. 

Either way, to those of us with a winter, it sounds like a good problem to have. 

My concern is that around here, fig trees don't necessarily go dormant. It is not unusual to have a warm sunny Christmas. At the same time, overnight temperatures an drop pretty low. I think these sudden, occasional frosts could potentially kill a small tree. If not, I think a frost might at least temporarily stunt the tree's growth. So, my theory is that if the tree can avoid these occasional frosts, I might be able to extend the growing season, not lose green growing tips to frost, and most of all, not kill the tree.

I'm going to guess that if I'm the only one thinking about doing this, maybe I'm on the wrong track? My trees look so healthy now, but they are still rather small. Earlier this Spring, I lost half of my newly potted cuttings to a late frost. Granted, they are much bigger now. But, still makes me worry to think of them out there on their own with no protection. Maybe I'd better keep them in pots until Spring and build a greenhouse?

Paul,
A simple "Tomato Cloche" might be your answer for occasional frosts. They are used to protect growing plants early in the season in colder zones. A Google search will return lots of different designs.  Good Luck.