I might be passing you, going the opposite direction. I'm considering Rt. 94/Campo Rd. I PM'ed Nostatic about a route that way and this is what he sent me:
Don't know 94. What I would suggest is going past/through Glamis on hwy 78:
http://www.glamisonline.org/directions.asp
If you've never been to serious sand dunes it is worth the side trip. Amazing place, and this is a great time of year to pass through.