Ok, if you can do this with straight IP tables on Linux, you can do this with MT (which is still Linux). You just have to learn the abstraction layers that MT put on top.
So, both IP addresses are from the same provider. You probably don't have to worry about the actual GW then. The provider already knows how to send traffic to either one of your IP addresses and how to deal with traffic FROM either of your IP addresses.
Unless your provider is doing something very whacky, this will work just fine:
add address=220.127.116.11/24 interface=ether1
add address=18.104.22.168/24 interface=ether1
Again, your provider already knows how to reach 22.214.171.124, so you don't need to worry about that. When you send traffic FROM 126.96.36.199, it really doesn't matter which GW IP you use, as the GW router will know how to handle it already. Once you have this in place, test it:
/ping 188.8.131.52 src-address=184.108.40.206
/ping 220.127.116.11 src-address=18.104.22.168
If this does not work, contact your provider for assistance.