”I wonder if any athlete has tried diving front-ways over the bar, with something like part of a dolphin-kick to clear their feet & legs over..?”

That was the style in common use back in the ‘60s, it was called the Straddle. I was very much into athletics during my years at Grammer Skool, and it was the technique I used for high-jump. The jumper approached the bar ar a very acute angle, took off from the ‘inside’ foot, and crossed over the bar face-down It’s a shame we can’t post photos here, I have a great photo of me aged about sixteen, going over the bar face-down.

https://en.wikipedia.org/wiki/Straddle_technique