It already has those (under the "Etc" heading), as part of the 1533 pre-defined timezones. Hardly limited, one would think!

EDIT: Well, okay, it doesn't have half-hour GMT increments, just the full hour increments. But Newfies and others on half-hour offsets can just find the entries devoted to them. Pretty much the entire planet is included in the timezone database.

Cheers