Well, I'm glad to hear about this, so maybe if I get blasted I won't be too surprised and let go of the handle. I live in the land of perpetual high humidity, here in SC, which might be why it's never happened. I've flown a whole lot of miles of circles. It'll probably happen today.
You don't have to worry about letting go of the handle, as the shock will not let you open your hand. If you have a blocked nose due to the sniffles or sinus problems, it also opens your nose........but I would suggest that there other simpler and safer remedies out there.
I think that one of the best static incidents I've seen was with Bob Hunt at the Spanish world champs in 2006. He took off, and I forget the maneuver he did when he got zapped, but he shouted to the judges "electricity.....electricity!!" Everyone thought........o.k.....big deal, so you're flying an electric model. No need to shout about it. Meanwhile, Bob was trying to point out that he was getting static shocks. In 2004 in Muncie (also the world champs) Billy Werwage had to quit flying during one of his official flights, and many people had hair looking like Einstein's!
We get a lot of static up here in Johannesburg at 5000 to 6000 ft. in the summer. Using a metal handle or adding a wire from the lines does help, but I've found that it depends on the soles of your shoes as well. Modern plastic type soles will still give you shocks, so if you want the whole deal, just fly with bare feet. However, if there is a big fat black cloud above the circle, pack up and stop flying, because you are just asking to ionize a nice path down to you for lightning to strike.
There was a good thread on this a few years ago on the Stuka Stunt forum. Someone mentioned that if you have these black clouds overhead and lots of static, then just fire a model rocket into this lot and the thick smoke (full of carbon??) will make for a nice path for lightning to zap the circle. He did stress the point that you have to retreat some distance away for the circle, but said that it was pretty spectacular! I don't think that I need to be there......I'll just check it out on You Tube!