universal client

I’m trying to build some sort of hotspot function on RouterOS, but I don’t wat all the feautures the standard hotspot brings, so I want to build some of them.
Does anybody know how the universal client function can be made?
The first part is working.. I have made a bridge device and on the bridge I have made an ARP NAT so that RouterOS will be reply on every arp request from any source ip with it’s own mac.
But step 2 is the one-to-one NAT, in some sort of way I have to make dynamicly an 1:1 nat with every client, with the client and a new ip from the adress pool.
Anyone who knows how this can be done?

Thanks in advance
p.s If you have an other sugestion, please let me know (turn on hotspot is not what I want, because I don’t want masquerading and no proxy server turned on)