You could do 4wd, but it does require 2 complete power systems (motor/ESC/battery). At one time I did have 4x4 Stampede, and I made a tutorial on how to do it:
http://www.4x4pede.freehomepage.com
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz