Had a bit of bother with this so I thought it may help others to see the solution, our provider gives us a /28 allocation and all along we have being doing 1:1 NAT. Its been on my mind for a while to sort it out and I have worked out the following solution.
The heads on the Mikrotik forum reccomend getting our provider to route the IP’s but this solution also works.
Proxy-arp on Wan interface does works as you suggested. But proxy-arp is bad, brings in loads on unwanted traffic, exposes your router to world arp scan and also stops working sometime.
You can find on mikrotik forum why to avoid proxy-arp
