me being the fool that i am, decided to work on trying to modify your 3dn. while nowhere near perfect (jumping being a problem still but more on that later), this is how it came out.
that jumping problem? my only idea on that is to use the Z position of the shadow itself and then use that to work out where on the Z plane the bike itself should be since logically the shadow should be underneath the bike. plus this modification makes the ram mapping issue moot mostly. Edit: fixed a couple of errant ramps and excluded any air tagged elements from the actual y algorithm (neither change reflected in the video)
either way, give it a go and see if my modification has made it easier for you to handle things.