So, if I've read this right, all the "bass" will be coming from the Sub.....
the door speakers will handle all of mid/top end.
If so, yes a crossover will do it, BUT......
Like others have said, it's an "out-there" way of doing it
Personally, I'd get some uprated stuff (3way) for the doors/pillars etc and still get a sub
Hope this helps in SOME way
Dan