Suggestion
I was thinking you should be given a very limited possibility of wishing for wish items, hence "postponing" the event.

• Wishing for a ring of djinni summoning would give you a blessed one.
• Wishing for a wand of wishing would give you a non-cursed one with 0 charges (having to wrest the last charge).
• Wishing for the above items in plural would give a "*ONE* SHALL BE ENOUGH" message, then do the same.
• Wishing for spellbooks of Wish would continue current behavior, as you can get more than one wish from those.

Why it'd improve the game
When you have to make a wish, no other actions may be performed. If you want to look or ask for advice here on the forums, IRC, etc., the game window must be left open. This leaves you unable to save the game and thus exposed to OS crashes or power failures. That is not a problem for veterans since it's unlikely that they'd come across a wish unprepared and not be sure of what they want, but for a beginner it might be different. If they were intentionally going to zap a WoWi/use a RoDS but change their mind at the last second, they can undo it, too.

Notes
All of this wouldn't be abusable (as far as I can see), since you spend one wish to get another one.