Well, why don't you just use a standard 8 foot long whip? If you mount is in the right place, you'll achieve almost 90% efficiency. Of course, you can't use mag mounts, trunk lip mounts, or other temporary mounts.
All this said, you might as well forget 10 meters until about 3 to 5 years from now. Oh yes, there will be an occasional opening, but if you want reliable DX, you'll have to come down a few bands.