hook up your modem to a switch and you can "sign-in" using the PPPoE software on each computer directly connected to that switch (which is connected to the modem).
Each computer would have its own static IP.
And a router connected to that switch could serve other users behind it via DHCP and NAT.
Here is a ROUGH diagram. I'm not good at text art.
-->asdl modem -->Switch (not hub)-l-->computer 3
l-->computer 4 /-->computer 5
There you go!
You're using all five IP addys. The drawback I see is that your LAN isn't so simple to set-up. The computers directly connected to the modem (via switch) would see the router and not the computers behind the router.
A lot of routers, like mine for example, let me assign a PPPoE sign-in to a MAC address.
But I don't think most linksys, netgear etc. routers do this.