Ok, I don't know how to do this. I'll have a poke about and see what I come up with.
On one you setup an IP, say 192.168.113.1 with subnet mask 255.255.255.252, on the other 192.168.113.2 with subnet mask 255.255.255.252.
There you go, two directly connected computers on the same subnet being told what addresses to use rather than allowing them to unsuccessfully decide between themselves.