[1.7.2] Only allow shift click from slot

The problem I have is that the player has a custom inventory but there should only and really ONLY (creative mode excluded) one item of my custom type (let's name this item ItemFoo) in this inventory. I have no problems registering the ExtendedProperties for the player neither with opening the GUI to display the items in his box and those in his inventory. As a quick reminder, in his box can be any count of this ItemFoo but in his inventory should be only one and also the item should not be found in the default Minecraft inventory afterwards (so don't drop it infront of him, etc.).

I saw the method #canTakeStack(EntityPlayer) in slot in combination with #onPickupFromSlot(EntityPlayer, ItemStack) in the class Slot. How should I handle this issue that I can't differ between shift-pickup and normal pickup? Should I check if Shift is pressed? (could one change this keybinding? Where do I find the correct binding?), should I move the checking to the Container? (I might program more than one Container, copypasta no bueno) or do you have any other interesting ideas you think I should consider? Please give me your feedback about this issue, thanks.

PS: Maybe a feature request??