No, because there's plenty of timezones for every offset. For example, at -08:00 base offset from UTC we have America/Los_Angeles, America/Juneau, America/Whitehorse, America/Dawson, America/Tijuana, and America/Vancouver.
So which one of those corresponds to -8 hours?
It would be useful to be able to return a list of corresponding timezones, then the user could use whatever means they felt appropriate to select from the list (the application, I imagine, would be the determining factor in what this would be used for)
Matt