L2TP Server on 2 ISP Connection

Hello All,
My MT is a L2TP Server and It has two ISP Connections. Simultaneously Some client connect it via ISP1 and some clients connect it via ISP2. Clients have dynamic IPs. It is possible on MT ?, How ?

Bye..
Adnan

General question is: How can I send responce packets to internet via same (received) interface (IP) if I have more then one interface (IP) address.