I don't think you could change it in one place. The system I work on for my job gets all date/time stamps from one procedure in one database. That's how we keep various servers in sync and it also gives us one place to modify the date/time by adding or subtracting hours.
But TheBeerHouse wasn't designed for this. If you only want to change it in a couple places that should be easy enough, but a blanket change is going to be more work. Start by making a stored procedure, and then plug that in every time someone wants to get the time.
If you need frequent updates it might be more efficient to store an offset value in web.config, or in a table. And just do the math against the current server time - this will avoid a lot of extra queries.