I believe the only way a temp table can take advantage of a user-defined datatype is for it to exist in the tempdb. The problem with this is each time the server restarts the tempdb is rebuilt so your datatype will dissappear. However if you need this datatype you can add it to model and each time the server restarts and tempdb is rebuilt it will return on it's own (like all databases tempdb uses model to build itself). The only downside is of course any new database you build will have this datatype in it.

"Don't roll your eyes at me. I will tape them in place." (Teacher on Boston Public)