I think the simplest solution would be to add an ingame parser that just reduces the results to Top DPS, no numbers just Who's First to who is last. If you see DPS-DPS-DPS-Tank-Healer-DPS-Healer-Tank as the top DPS rankings, then you know there is an issue with X DPS.

I think the biggest issue with a full on parser that gets to the micro of your Damage over time just puts to much focus on squeezing out every bit of damage. if the 4 DPS can remain in the top 4 spots, that should be good enough, if it's not, then the group can work down on what they can improve. No numbers, just 4 DPS fighting to get top spot, or 2nd.