Fix the real problem in this case. So for your PBR for other traffic/network, is the remote knows to reply to that src_network via the WAN2 vrs MPLS cloud?
If I' m missing something from your simple but effective diagram, the left FW1 is routing over WAN2, so how does the rightside FW2 know about the 192.168.2.2 server?
Can you place a " static" route on that firewall that says to use " wan2" to reach that host ? Or are we missing something? Route selection be via most exact match, so FW2 will say to reach this host use my WAN2 and for all other traffic in the 192.168.2.0/24 network use the MPLS
If the later is doable, than RPF checks & maintaining statefull-checks would not be an issues and will still pass.