First off, let me be clear. I've never done it.
Having said that, it's not easy at all. You need to shift with right hand likely since the left works the clutch. Meaning your linkage or whatever has to move to the right side. The engine does not lend itself to that as the shift lever shaft does not go all the way through the engine to possibly attach to the other side of engine like some do. Additionally, shifting by hand is not nearly so seamless as by foot, the foot has much more power behind it and doing it by hand will be very distracting with that.
Might make it easier to do by using a rocker type gear change lever, one you push down on the back of rather than lifting the front. That way all the shifting is by pushing down only.
Ever think about swapping bike out for an automatic model? Much less shifting there. Hard to find them though.
Look around at some of the injured but still riding Harley guys' stuff, many of them devoted enough to do that, I've seen the gear sticks that stick way up in the air to make it easier to lever the next gear into place. All custom one off work there.
You won't find a bolt on aftermarket setup for that as it would be a legal liability issue that would bankrupt a company out of business in hours if not days. You just might find a rocker lever though, some cruising types like them.