Technical Grappling - Climbing on Opponents

[Barghaest]

I did a few searches and turned up nothing on this subject (surprised it wasn't asked, maybe I just missed it) and even the Technical Natasha didn't really address it.

With the various stability rules and other factors in Technical Grappling... how would you handle someone climbing/jumping on their opponent while they are still standing?

This might be more common in cinematic campaigns, but it happens enough in real life to be somewhat addressed: a smaller opponent - be it less SM or just a person with a slighter build and same SM - jumping on someone's back as a forced piggyback (grappling the torso with the legs and often the neck/head with the arms, although they might leave one arm free to beat their opponent on the head)... according to stability rules this might be considered under the exception detailing the "side mount" but I assumed that still implied contact with the ground for providing stability, so I'm wonder how this would be ruled (I assume they'd be considered Unstable, at least, if not in danger of falling prone) and what mechanics a person would use to handle it (skills involved, what penalties, how it affects opponent, how it affects attacker, whether it's a technique/combination/AoA-variant, if it includes Weight Advantage, etc.).

Apart from the above example (which everyone has seen probably seen happen in RL at least once), there's also the more cinematic act of jumping on someone's shoulders and grappling their neck with your legs (most often seen performed by females in film/video-games so my circle of friends has taken to calling it a "Flying Muffocation" after Keiko Kamen's signature move - also used by Cammy in Street Fighter and Black Widow in Iron Man 2) often followed by a takedown.

Dave's example of this in Technical Natasha detailing the Acrobatic Double-Leg Grapple is great, but lacks a few details I'm interested in... mainly, if you fail on the attack roll what happens (would you treat it like a missed Jump Kick)?
If it's not immediately followed up in a combination, does it have any special effects on the opponent's following round (especially since he's supporting your weight now) such as making them Unstable?
If an opponent breaks your grapple, will you automatically fall prone - basically giving him almost a free Judo Throw effect on you - or would you remain on his shoulders until he dislodged you another way?
How would mechanics be handled if you used your arms to brace against the walls (say in a narrow hallway) or held on to a beam/pipe overhead?

Any suggestions (or direction towards specific rules/posts/examples) would be most welcome!