Require product on condition


Is there any possilbe way to require a product ONLY is a condition is met. Such as a checkbox being checked? I need to have the ability to apply a one time fee to an order. I have tried several methods such as using a promotion to counter the required product (I don't like this way), product configurator and product options. The last two add the cost varient/products to equal the quantity of the order. So if I need product B required on product A and I order 10 of product A I need to have 1 product B required only if option 1 is checked.

Can anyone help me out. I am completely lost with the documentation to create an addon for this small action but if someone can point me in the right direction for that I can go that route.