Aaron Berquist gives us a SQL Script to Quickly Add Users to POWERUSER Role in Dynamics GP 2010. This is really designed for use in test systems, not production.
Quickly Add Users to POWERUSER Role in Dynamics GP 2010
Install, Upgrade & AdminGP 2010
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.