Site Discovery finding VPN IP instead of BlackBerry IP (tethered)

We have users that connect to our VPN (Cisco client) through their BlackBerrys tethered to their laptops(Win XP) when they are in the field.  The subnet that takes over the computer is the BlackBerry ISP IP and we can't configure every BlackBerry/ISP subnet in our Site Discovery.
 
Does anyone know a way that we can get Site Discovery to find the Cisco VPN connections IP?   Then we can simply just put that VPN subnet into Site Discovery and then SMS can work with these remote systems.

I found perfect vpn for blackberry provided by SuperVPN. I followed instructions they sent me and now everything works great.