FYI- a professional rigger came up with a solution that is quite easy and looks very good. He had some very large diameter (>1.5" dia.) heat shrink tubing, the kind used to seal electrical
connections. You just slip it over the 1.5" OD fitting and when heated, pulls down very tight over the fitting. The final diameter was such that it had to be worked into the 40mm ID waste tubing. It turns out that there are two wall thicknesses of the shrink tubing. Be sure to get the thinner version. The thicker stuff gives greater than 2 mm increase in OD. This stuff is very tough, water
resistant but soft enough to clamp down.