Counting MQLs

In our smart list for defining criteria for MQL threshold, we're currently unable to add "was added to opportunity" as a filter because Marketo counts opportunities at the contact level. So if an opportunity has 5 contacts associated, it would increase our MQL count by 5 instead of 1. 

So looking for alternate approaches to be able to give marketing MQL credit for opportunities created, but not inflate numbers.

Thought about using "was added to opportunity" AND "is primary contact" to ensure that only one contact gets counted per opportunity. But reps aren't disciplined in designating primary contact for every opp. 

Currently, we do not add to score for when someone is added to opportunity. Was thinking of using that, but would probably hit same issue as every contact associated with opp would get the lead score bump that would count them as MQLs.

So just wondering if anyone has any suggestions?

Thanks.