I am not sure what you mean by a staging area. Also it is only about 5 hours from SD to Deva. Is it really necessary to stop an hour or so earlier? Anyway there are plenty of places to boondock from Baker to Deva. You will be coming in on the Eastern side as the quickest route.
If you really want to cut the driving time, you could spend a night at either Joshua Tree or in the Mojave Preserve. You can boondock in numerous places outside of those areas. I have stayed at the campground in Mojave but typically just boondock in the preserve.