I'm concerned about your safety if you install the tarp. I've never heard of this method and don't give much credence to ehow, but ..........if you do it, you'd have to do it in the dark, after the yellow jackets have returned to the nest for the night.

I'm in Georgia. Don't find the yellow jackets to be aggressive unless the area near the nest is disturbed.

Hope you'll get more advice, also hope you'll post your results.

Putting a tarp over that "compost" pile will not be enough to smother that nest and they will simply find another way out to continue doing what they do, if they do not already have a second entrance/exit in place.
Talk with the people at your local office of your state universities Cooperative Extension Service who may have some ideas on eliminating this nest.

Thanks for the feedback! I guess that we'll put up a warning sign for the party, avoid mowing there, and just wait it out for a few months.