Config PPTP server with Multiple WAN IP address on single interface?

Hi

i have 1 wan interface with 2 public addresses with same gateway and there is one inside lan subnet on eth2. users connect to the internet with pptp vpn
i would like part of my pptp user’s go out with one IP address and other user’s go out with another.

I’m not mikrotik expert but i like to play with it.

please anyone can guide me to solve this problem?

Thanks in advance , any help will be very well appreciated.