TBH, I think I might have been able to do it if I had fully committed to it, but if you examine the photo carefully you might be able to see that I had Look pedals on the bike and therefore had big plastic cleats on the soles of my shoes. I was worried that if I had to do an emergency dismount nearer the top, my feet would slide from under me. This worry turned out to be realistic because I slipped and nearly fell when walking back down the hill to take that photo!
I have now got mountain bike type SPD pedals on all of my bikes so my shoes have recessed cleats for safer emergency bailouts!