Just to be clear, I realize some of us cannot prone paddle anymore.
But prone paddling on a long SUP is very different than on a sinking shortboard. I could not prone paddle more than 10mn at a time a 7'2" prone surfboard, but once I had to get back from an outer reef prone paddling my 10' longboard SUP with some wind after breaking my paddle, and I could paddle 30mn without stopping by using some paddeboarding techniques that I had read about or seen, even though I never paddleboarded myself.
Since the 10' SUP board glides between strokes I was able to rest one arm and my chin on the board while paddling 3 to 5 times with the other arm. At the end of the 30mn, I felt like I could have continued for hours this way. I guess other paddleboarding techniques could be useful, such as knee paddling (with knee protections?), or hand paddles like Dave Kalama uses?