Using BOGO pricing rules for more than one product.

I'm trying to set up pricing rules that would allow a patron to, for every four tickets purchased, get two of those seats comped.

I have gotten it to work where for every four tickets purchased within one performance, two of those will be comped. I'm attempting to find a way for this to work where all four tickets would not have to be within one performance for the pricing rule to be applied.

For example, a patron buys one ticket to four performances, is it possible to have two of those comped? 

Thanks everyone!