Love this post.
I think the best way to learn is to sort of simulate the position but without the leg over the bars to start off with. If you try to lean as forward as you can into the bars with your leading leg sticking out straight (but don't worry about it going over the bar) and use your trailing leg to force the pedal still, you should be able to skid due to your weight being forward like @M_V says.
Once you get used to skidding one footed like that, then I'd worry about doing the leg over bit! That's how I was taught at least.
It sounds like you're struggling with the initial skid bit, which you should be able to do without the leg over before you proceed!