e-commerce quantity

I have a generic product that I created to use for deposits through an event signup module. I'm running into an issue where one user will sign up for a group. So instead of having several users sign up individually I have one user modifying the quantity at the checkout screen. This is throwing off the available event slots in our inventory and I'd like to disable this option for this product. Does anyone know a way to prevent the user from modifying the quantity for a specific product?

I'm using e-commerce 5.x-3.5 with Drupal 5.x.