Timezone into/out of function

Hi,

I have two functions that have a timestamp wtz passed to and return
timestamps wtz in a refcursor. The catch is that I need the timezone on the
timestamp passed out to match the timezone of the timestamp passed in. I
realize I can set the timezone parameter before making the call, but I'm
concerned that if a user calls it with a timezone that is different than the
timezone parameter the date they get won't match the timezone they
requested.

Is there a way I can specify timezone as a parameter and force the
timestamps in the where and select clauses to use that timezone? (without
having to set the timezone parameter in the session)

Thanks

Jed.