I agree. (If you mean that you should be able to give your puppets some of your area, that is.)
I always thought that it was odd, that in Victoria you have a different map for releasing dominions, showing the future dominion, but they had not made a "province chooser" for it. So that you could click on province "On/off" for joining the Dominion or staying in your regime. (This especially usefull in Vic, because the dominions only had cores on the provinces you gave them, not their historic cores).
So in short, what I suggest is:
When you press the "Release puppet" button, you get to the diplomatic map mode and you can see the puppet you are about to release, and during this time you can click on provinces to give them away or take them back. (Click once goes to puppet, click again comes back, click again goes to puppet...)
A flexible, easily codable and very, very awarding system.
A similar system could be used with sharing territory and land with allies: Choose the ally to change with, go to the "Diplomatic map", begin clicking... Send the supposed change.
(Ie, if someone did not get it yet, I mean that when you click your province once, it changes to the puppet`s colour (And will be released for the puppet, if you press OK), click it again and it is back, etc, etc....
The map modes are not binding, not until you press the OK button, which in case of releasing puppet, releases the chosen provinces, or in the case of chaning territories sends the proposition to your ally.