There's a couple ways to do this, but yes it's doable.

One way is to create a Integer field to represent the dollar value the user has earned. You'd then create a CBSubs Promotion that uses the integer field as it's discount value. If you need math to calculate points to a dollar value you could use a CB Query Field to use SQL to pull the integer fields value and use SQL functions to calculate the dollar value. You'd then use the CB Query Field as the promotion discount.

Another way is if you're using a 3rd party point system you could use a CB Query Field to pull the points, calculate a dollar value, then have it be the discount field for the CBSubs Promotion.

Note for query fields to work in CBSubs Promotions I believe you need to set it to "fixed amount" then substitute it in.

Another option is to develop a new payment gateway that handles its payment process through some sort of points system.