Raze - the way I ended up 'solving' the problem is that it's possible (a bit tricky, but seemingly less hard than the platform) to land on the force field device which is also at the bottom of the shaft. That is at a different angle, and much lower than the original platform, and it's a pretty easy jump from the device to the platform.
As for stepping off, that doesn't work - I tried it at least twice. If you just step off the top platform you start from, you will fall straight down, and just barely miss the platform, falling into the lava.
I had given some thought about doing a jump at a 45 degree angle towards the wall - I would have tried that next if I hadn't been able to land on the generator.
