Rampage Paintball Ltd

When I make up the add-ons to add to the appointment types I am able to detail every extra cart item I want to add, however I want the customer to be able to take more than 1 add on, but I cannot see if there is a way to make this a number instead of a box they just click to get 1 item. I would like the customer to have the option of getting more than 1 type of add on of the same product.. Anyone know if this is possible to add on multiple add ons of the same item?