Not to beat a dead horse, but ultimately you need to find root cause. SQL Server uses the TempDB to perform sorts that don't fit in memory. Most-likely you have some queries that are poor... unneeded order by clause, nested-loop joins instead of hash joins, poor use if subqueries. Or you may find that it's due to the shier volume of data being sorted.

If the disk sorts end up being a necessary evil, then you can look at getting tempdb onto a disk with plenty of room to grow, and/or adding more memory to the server.

Let me know if you need any help looking at the queries.