Works great, sebastian, thank you very much! I'm just missing a couple of things and the system will be exactly how I wanted it:
1- I can't remove an item via right click. Under "Mouse properties/Right mouse button" I created an action with these steps:
call action "cur_default"
change condition item_used to false
execute a script 'oldItem=nil'
I thought this would do the trick, but the current item remain set until I left click on something;
2- Is there a way to keep the item set until the player press the right mouse button? Let's assume the player is stucked and wants to try every item on every object in the background (we all did that!), I think it would be annoying for him having to always click on the item in the inventory!
Basically what I need to achieve is the player to be able to remove the item ONLY via right click!