Lock charged weapon to slot 1?

As part of my ammo system (based on Grater's orb-based system), which involves both weapons and ammo, I need a way to prevent a character from using a charged item to "fuel" his attack; for example, if a character were to have a 20-shot weapon and switch it with a charged item while he's firing.

Is there a way I can make slot 1 for weapons only, not even other charged items?

(At the moment, I modified the trigger so that as soon as the weapon runs out of charges, it's replaced in the slot with an Unloaded Weapon. Ammo clips aren't charged but have one use of a modified Channel; I'm gonna trigger it so that using the item/ability will remove the clip and replace the Unloaded Weapon with one appropriate to that clip's type ...)