I'm not sure how to do it as a standalone thing...
But if you're using my Compact Headers templates, you can also use my UBB Headesr & Footers via SSI hack. It brings the register/login info from UBB onto any SSI-enabled page. You do have to be using Compact Headers, though, because the login info is not part of the variable the SSI calls in a normal installation. You can see my homepage,
http://www.se7enet.com/index.shtml , for an example...
---Skorpion