Completed your surveys, but for the forum... The device you describe in the surveymonkey survey would increase the radius of the handle, which would increase the off center pull due to the physical makeup of the hand and wrist that causes the friction on the drive. That would seem to me to increase the problem, not to mention just the larger size of the handle that may be uncomfortable. Until someone comes up with a handle where you can pull directly in line with your wrist to eliminate that 3/4" "moment arm" that causes the friction on the fingers, friction will be present, blisters will develop. That, of course wouldn't work in OTW rowing because you have to feather the oar, which requires that slight moment arm to develop torque to rotate the oar.
I use baseball batting gloves, which are cut to fit around curved shafts and are thin leather, so they work well on the erg handle. I found that sore hands and blisters in general, have subsided since I started using slides on the erg, which reduces the sharp forces at the catch. That sharp little twisting motion due to the 3/4" off-center grip of the fingers around the handle is the main cause, no matter how loosely I grip.
Mark. Rower first, cyclist too.