Routing over alternate network

[markdueck]

First of all, I'm not sure if my title is correct.  My situation is this:  I have 3 locations, connecting through VPN to a central server (A).  Unfortunately the central server is on a leg of internet that is not very stable.  I have now created a direct wireless network to connect one location (B) to the central server (A).  Location C  however cannot connect directly over wireless, but the network between B and C is more stable than from  (B || C) to A.

My goal now is to create a second VPN from C to B, and then route at all C traffic at B through the more stable Wireless link.  Is this understandable?  If not I'll try to do a drawing of it.

Can someone give me hints/ideas how to go about doing this?

PS.  B to A  and C to A are all ClarkConnect routers, while my VPN between A and B is on Soekris 4801 running pfSense.  I want to use 2 Alix boards to do the additional VPN between C and B.

Thank you.