One possibly simple solution is to increase environmental humidity. Very effective if you can do it. I've noticed static charge is most noticeable during the winter when humidity levels are low. Get a humidifier.
I'll show other solutions to permanently solve the problem at the end of this.
The part I don't understand is why a spinning belt builds up electrons. Something is giving up electrons like rubbing wool against a balloon. Wool gives up electrons that collect on the surface of the balloon causing the balloon surface to carry a negative charge. In other words, electrons transferred from the wool to the balloon.
It appears that the back of the belt rubbing on the platen might be the source, like wool is to a balloon.
Looks like spraying the back of the belt with anti-static spray solves it. If that works that is a really easy solution.
A grounded wrist strap is common when working with electronics. Not so good around spinning equipment. I'll post a link at the end of this where in the comments one guy uses a grounded ankle strap. Seems like a pain in the butt to me.
Static charge from belt grinders is very well known. If the charge is sufficient enough it can cause the operator to jerk and flail in an involuntary spasm and can actually be dangerous around machinery. If you are flopping around like a fish on the beach when sharpening, it's probably best to resolve the issue.
Apparently the rotating belt is the source. Electrons are transferred from the belt to the operator through the knife. Like the surface of a balloon rubbed with wool, the operator becomes negatively charged with electrons like flies on, um... well you know. When a grounded surface is touched, all those electrons move to the grounded surface. And, they do it in a BIG hurry all at once. POW! ZAP! A first hand demo of electricity 101.
Here are two links. The first offers permanent solutions and an explanation of what's happening. The second shows the principals involved.
In the following, read the comments too. Some info there.
http://dcknives.blogspot.com/p/static-di...inder.html
The following is a cool demo of what's happening. It takes a while to load, so just let it finish. Once loaded, drag the balloon and rub it over the sweater. You can then move the balloon over to the wall. A great visual demo of what's happening.
https://phet.colorado.edu/sims/html/ball...ty_en.html
If the anti-static spray thing works that's easy.
Would wearing rubber or nitrile gloves work? Both are insulators and would build up electrons like the surface of a balloon. Nitrile gloves are very thin and I suspect you would still feel it when the charge is dissipated. Thick rubber gloves would work, but who wants to wear them when sharpening.
Probably a permanent ant-static brush installed on the grinder is the best long term solution. Hmm... accessory for the Kallyrest? Or, get a humidifier.