The old-timey sticky fly-paper still works reasonably well. Somewhat unsightly.
Goodness! Well worth asking. So many bright and knowledgeable folks here.
Fortunately gnat season appears to be over.
But, lots of ideas presented here to try, if gnats come back next time around.
The very small spritz of alcohol seemed to work pretty well. That at least stops the moving target. Then wipe them off the mirror with a dirty t-shirt or such.
Thanks for responding!
Nicholas Kormanik
Also provides for some good iNatting opportunities to record the different insects unluckily stuck on the trap!