well the easiest thing to do would be outbound NAT on the LAN interface, source of the openvpn subnet, translated to the LAN IP of the box.
Yes, you'd have to switch to manual.
You could do 1:1 NAT on LAN from an OpenVPN IP to a VIP (non-CARP!) in the LAN subnet, but that would only work for one client with a static IP.