I haven't seen any of the videos, or read all the comments, so sorry if I repeat any methods.
My gelding is trained to me raising my hand, and if he's a little confused (which sometimes happens if I mount from something strange), I'll refresh him with the command "over".
I just stood on the mounting block, him standing straight to it. With a lunge whip, I would just tap his HQ, and cue with "over". With a tap on his QH, I'll praise with each lateral step he took towards me, and let him stand to think it over. Then another step, then another, slowly, until he's standing aside to me, so I can mount. I make a point of actually mounting every time, once he's over, so he connects me mounting, to him sidepassing over to me on the mounting block so he doesn't get bored, and not see a purpose to the exercise.
Just keep doing that, then over time it gets quicker, and you can take the stick away, and then eventually, you just hop up on whatever you're mounting on, and hold your hand, up and they sidepass right on over to you.
It took my gelding about two weeks, to quickly and independently sidepass over to me. That was with working on it about 3 times a week, so six sessions, and he had it down.
"You're just as sane as I am."~Luna Lovegood.