I'll wait for the after action report before I say 'good job', Russ. Duct/Gaffer Tape on knee pads works well, definitely, but I have my doubts about the glue/bandage interface and also about how well the bandage will stay in place with the pad attached. I have worn tubular bandage under kecks to prevent the straps for crap knee pads, which bunch up in the crook of the knee when they slip, from giving me the dreaded chafe - it isn't as immobile as you'd want TBH and that's without any added weight.
I think the best solution may be to add pockets to the inside of the kecks and fit sleeping mat foam faced with a layer of plastic washing up bowl inside. Although the bagginess of the kecks will work against this as a plan. Maybe some plastic with a preformed curve, so that even if the pad isn't central when you kneel, the shape will make your knee slide into the pad. Couple of layers of 2L pop bottle may do it