multiple nating with fake ip pool???

I am use pppoe server on LAN Port 50.50.50.0/24 Nat with my 123.225.31.2/29

i want multi nat

123.225.31.3/29 use 50.50.50.1-15 pppoe user (Per 15 User one Public ip)
123.225.31.4/29 use 50.50.50.16-30 pppoe user(Per 15 User one Public ip)

can it is possible???

Please Anyone Reply