Well, with the newest beta of Ply's Mod, we have the fix that Lee put in to allow the "plrdrop" command to work, so if the weapon was picked up in the same level, you could script it to be dropped when the player presses a certain key.
To keep ammo the same when you pick it back up, you may need to have the initial weapon pickup have 0 ammo, and the player gets ammo a different way.
In another way, you could alter the script so that the FIRST time the player picks it up, it gives them ammo by altering the ammo pool variable that you gave to the weapon. Subsequent times it is picked up will not give the player ammo. (For this one you will also need to set the weapon pickup's "ammo" or "clip amount" to 0 on the entity so that the ammo given is specified by the script)
The one and only,