two VPN with two WAN (no solution?)

Hello Everyone!

i am attached simple diagram.
Router have two ppp out, used two modems with HUB. How to create two VPN tunnels with different ppp to one dedicated IP (vpn server)?
2vpn.gif

i mean this issue not solve by routing because VPN server have one IP. Correct?
But how to solve this with mangle? how mark out vpn connection for routing mark?