@Mavhack Sounds like you need a feature request submitted.  I honestly don't blame the router for rejecting a /32 as a WAN IP though...I mean, where's the ISP's router IP in all this?  Your ISP is breaking the rules probably to prevent folks from getting multiple IPs for free, but that doesn't solve your immediate issue.  Because it's DHCP...if you don't do the dance with the DHCP server, it will just give it out to someone else...  I'd call your ISP and ask them to rethink their design ie allow you to statically configure your IP.  I have worked for an ISP, and in those cases they handed out /30's, the four IP's being 'Network, Gateway, UserIP, Broadcast'....but it's wasteful of the IPv4 space and the configs were all static anyways.

I would love to learn details of it, but I do not think an ISP would require this kind of setup from their customers. That would not work for most, if not all, of them. The subnet mask 255.255.255.255 is used for point-to-point links, for example PPPoE. I also suspect that an ISP may use it internally with termination devices which they supply and require their customers to use.