Simple multi wan setup, managing what host uses what wan

[CDIMMO]

Currently i have access to 2 isp's and i am required to have redundant hardware.
I have 2 wans set up, however i do not want to set up failover, instead i want everything to connect to the web via Wan1 and I want a couple specific nodes (using static ip's) to connect to wan2 only, im assuming i can accomplish this with an outbound nat rule? how do i set that up?

to complicate things just a little i am using Carp, but wan2 is not a carp member and rules related to it are not synced.

current settings are
wanA upstream xxx.xxx.xx.169/29
wanA vip xxx.xxx.xx.171
box 1 wanA ip xxx.xxx.xx.172
box 2 wanA ip xxx.xxx.xx.173

wanB upstream xx.xx.xx.2/24
box 1 wanB ip xx.xx.xx.23
box 2 wanB ip xx.xx.xx.24

lan 1 vip 192.168.1.1/23
box 1 lan ip 192.168.1.2
box 2 lan ip 192.168.1.3

sync interface info not included. I am not using the carp failover for wanB as I want carp to switch over only if our primary isp is down.

how do i make the device with the lan ip address 192.168.0.21 use wanB instead of wanA like all other traffic