I was guessing.. as ip are assigned by dhcp (so dhcp can add arp dynamically) probably the arp-reply method could work too. You say 1:1 nat needs full arp functionality but probably that is enough, did you test it?
Now we're talking about it... I think you're most likely right. I had the feature in mind that allows clients with different static IPs to access the network. But in this case, I'm now almost sure that it'll work with static arp as well... No need to catch foreign static IPs. Good point!
-Chris