Just a quick thought before I run through a profiler/Perfmon/custom logging process, assuming you are running SQL Server 2005 or 2008, try running this command:

use [tempdb]

go

select

OBJECT_NAME(object_id) [Object Name],

SUM (reserved_page_count) * 8192/ 1024 [Reserved_KB],

SUM(used_page_count) * 8192 / 1024 [Used_KB]

from sys.dm_db_partition_stats

group by OBJECT_NAME(object_id)

order by reserved_kb desc;

It will list out all the tables currently available in the [tempdb] database and there space allocation stats, maybe you could use this to trace a table with a large allocation back to a stored procedure?