You're already paying them. Simply tell them to do this during any downtime they might have. Obviously don't encroach on their lunch/home time, though.

Or, strange concept, the employees benefit from their efforts to improve the company, and idea of working during lunch on a trival task makes sense if they don't have anything else worth doing.

>the employees benefit from their efforts to improve the company

The traditional benefit for this activity is known as a "pay check".

Be wary of someone who tells you that changing the world should be its own reward when it looks like they'll be keeping the money.

its no longer a break if you're still working.

And the break is worth doing. Do you want your highly paid managers, engineers, salespeople, etc. properly recuperating? To better tackle the nontrivial tasks you pay the big bucks to tackle?

Or do you want really really expensive mechanical turks?