Hi
I was interested in your question, and did a bit of research. - However I don't think there is a way to access the timezone offsets from within SQL Server,
I think you will have to write a new the function and pass a location parameter - and either hard-code offsets, or create your won timezone offset lookup table - there must be a standard for this somewhere.
and while looking for a standard - I found this, which seems to cover what you want.
http://blogs.msdn.com/b/sqlprogrammability/archive/2008/03/18/using-time-zone-data-in-sql-server-2008.aspx