I had the same problem as you have: a temporary tablespace became too big because of a wrong sql-statement.
It's better to limit the growth of the temp tablespace. Just let that SQL-statement fail! Otherwise your server will hang if the harddisk is filled up with temp-extents...
Also the statement you mentioned (ALTER TABLESPACE TEMP DEFAULT STORAGE (PCTINCREASE 0); ) is known to me: It's a way to trigger Oracle to flush the temporary tablespace.
I tried it once and after that SMON started to work on the ts. After SMON stopped (visible through the Task Manager of W2K) I tried to drop the TS, but somehow Oracle didn't want to release it. Oracle has some kind of handle with the ts.
I had to bounce the db before I could drop the damn thing.
If you really want to schedule it, then you could try to execute the statement via a PL/SQL procedure. But be sure the procedure is started by a user that has the right privileges.