Now, you can stand on it with care, and the crank won't turn.
A bit of bouncing with care can be applied too.
So stand on the spanner, if I understand correctly? That's about the opposite of what I've been doing - using my foot to hold the pedal steady. Trouble is, I think the axle's now so rounded off that the spanner will just slip.
Yes, that's absolutely what I mean.
If you set up the geometry of what you're trying to do as I described, the crank won't move, and you can stand on the spanner.
I'll see if I can manage a photo...
Here's how to set it up:
And here's me horsing on it:
Notice how the geometry is such than my foot is pushing directly towards the bottom bracket, so I'm producing almost no turning moment on the crank, but lots on the pedal axle. I'm aiming to have the end of the spanner almost directly above the BB, but slightly forward, so the residual moment on the crank is trying to turn the crank forward, which I hold against the brakes. Avoid having the end of the spanner to the rear of the BB, because the residual torque is in the free-wheel direction, and can result in a shin-whacking incident.
This is really easy to do, and you can generate a large amount of well-controlled torque.
Not much use if you've already rounded it, tho.
Oh, and regarding the Allen key hole in the back of some pedal axles: You'll bend an Allen key long before you shift a stubborn pedal.