We have a a promotion for a "Family Four Pack" for one of our current shows. It uses Pricing Rules AND a Promotion Code.
While this particular discount is a percentage I see that you DO have the option to toggle the switch to be a dollar amount instead.
For our case we used the following in the pricing rule:
Doing this, coupled with creating the promotion code for us allowed us to hide this pricing rule behind our promotional source code. We've also gone a step further to make sure that our source codes are mapped to certain modes of sale for on line use. It's a bit of a set up, but for us it works.