If you want to assign a direct public IP to a hotspot user, you have two options. The best and easiest one is to have a public IP subnet routed to you by your provider, so that you can assign those IPs to your LAN interface, and use them however you want to.
The second option is an ugly hack that can cause a lot of problems. It is using proxy-arp on your LAN interface. Before doing this, first call your ISP and make sure turning on proxy-arp won’t mess them up, then you will also want to make sure there are no other devices on the WAN side of your router that are attached, as proxy-arp could cause them problems with IP confilcts. If both of those situations are fine, set up a route with it’s dst-address of one of your public IP addresses you want to hand out with the gateway set to the LAN interface.
You may need to do some more messing around to get it working just the way you want past that, but that will allow you at the very least to assign a to-address of a hotspot user a “real” public IP, if not being able to assign them a public IP via DHCP.