Looking for non-TZ-dependent localtime()

I have a multithreaded server that has a thread per client, and needs to talk to clients in their local timezone. All the "normal" UNIX time functions rely on "TZ" for timezone information, so even though they're nominally "thread-safe" they don't support my application, since TZ is global across threads. Is there a localtime()-like implementation out there that can do what I need, or do I have to write one? And if not and I have to write one, what code base is the "correct" one to start from (e.g. Linux, tzcode2003e.tar.gz from elsi.nci.nih.gov, etc.)? Thanks, -- Michael Lindner