Vent Insert for your Central Heating and Air

I love the smell of warm bread, I love the smell of fresh basil, (don't be scandalized here) I love the smell of fresh coffee with caramel and whip cream.  So why can't I just stick those things in my vents and get the fresh scent of whatever when I want it?  They make huge HVAC scent systems for the diffusion of sweetness in public places but all I want is a little door in a vent close to the furnace (so the scent gets to the whole house) that I can slide scent sticks or those colored pine trees for your car into.  Then you could change what you wanted as the season changes or company comes over, etc.