Timezones In Select Statement

The situation is that I have a query where a [thing] is supposed to
end, in the sense that I don't want it to be pulled back in the query,
at a certain time (end_date), but that is determined by the timezone
that [thing] is located in (end_timezone).

Basically, I want to say:
1) If the current record has a timezone not equal to the current time
zone, which is mountain, then change the end_date being pulled back to
reflect the time zone
2) Then, only pull back records that are scheduled to end before that
time.

I know this statement isn't valid, but I'll post it here to try to
convey what I'm attempting:

select end_date, end_timezone,
CASEend_timezone
WHEN 'ET' THEN DATEADD(hh, 2, end_date)
WHEN 'CT' THEN DATEADD(hh, 1, end_date)
WHEN 'PT' THEN DATEADD(hh, -1, end_date)
ELSE end_date
END AS theEndDate
from offers
where end_timezone = 'PT'
and theEndDate >= {ts '2006-01-31 14:01:27'}

Of course, this statement fails. Any suggestions on how to do what I'm
trying to do?

Thanks!