There are many ways to do that, I will give a couple ones.
First option, multiple virtual servers.
You could create multiple forward virtual servers with destination 0.0.0.0/0 and source as the server ip, and with the snap pool with the IP you want.
Second, single forward virtual server, and irule + datagroup.
The iRule would perform the snat based in the source IP and get the snat IP from the datagroup.
Some useful links for that:
https://support.f5.com/csp/article/K14800
https://devcentral.f5.com/wiki/irules.snat.ashx
https://devcentral.f5.com/wiki/irules.class.ashx