Simple answer: Wait for the Omega version of the Catalyst drivers.
Detailed answer: One of the modifications Omega did was to add 1280x960 to the resolutions recognized by default on driver installation (check the readme, it should be mentioned, I'd think). To do the equivalent, you'd have to modify the .inf file (which contains these resolutions) and reinstall, or simply modify the registry in the appropriate place to add the custom resolution. The latter is the quickest way, and it can also be done easily by installing a "tweaker" that supports custom resolution additions, such as Rage3D Tweak, which will offer you a GUI where you just pick the resolution and enable it.