I really don't see the problem. If the pilot asked for Pushback clearance BEFORE selecting the option in GSX, the controller can give it to him, and the pilot can then take all the time it needs, without requiring the controller to wait for him to confirm the direction.
The issue is, you cannot be 100% sure of what directions the user has available in GSX, because they depend both on the scenery AFCAD used and by a possible customization that user has made in GSX (or we made, for example when using an FSDT scenery on a stand that has a custom pushback), which might be way more complex than just Left or Right, considering that GSX now allows users to specify custom pushback locations.
The issue also works backwards: you, as the controller, might be aware of a real-life procedure that the pilot using GSX might not have at his disposal, either because the AFCAD doesn't support it, or GSX doesn't support it without an user customization, or GSX cannot support in any case, because the procedure is very unusual.
So, the real issue is, unless we'll had a way to ensure the kind of pushback you are clearing the user to can be performed by GSX, it doesn't make much sense to clear him to any pushback procedure (other than generally clearing him to "some" pushback), and just have the user confirming his own pushback intentions, clear him to do it, and let him do it, so he'll then start the GSX pushback, using the choice he asked for.
