Exit node multiple IP's

My ubuntu server (exit node) has 2 IPs and I want to use them separately. Is it possible to set some machines to use a specific IP from the exit node?
I have one exit node and the server has 2 IPs. I have 30 machines that want to pass their traffic through it. I want one of the IPs of the exit node to be assigned to 15 machines and the second IP to the other half.