Please report dangerous drivers to the police - Roadsafe. Report to plod, not just whinge here.

Looking at that, if he'd picked the bike up, he would have been OK, as carrying it over the line isn't propelling it...

I doubt it, you're still propelling it as it's not moving of its own accord. If you gave it a push and let go before the line and caught it after the line you've still propelled it over the line.

Ultimately the real answer won't be known until someone does it, gets an FPN and then challenges it in court. If a judge then decides that pushing/carrying/throwing a bike over the line is still "propelling a vehicle" then there's the required precedent in case law. Or it goes the other way and everyone does it until the legislation is amended to close the loophole.

Even if you manage to find a technicality (where the stop line is on a hill and the bike will move over the line due to gravity and not your propulsion) for this particular problem the Police can still consider other offences under the Road Traffic Act 1988 (as amended by the Road Traffic Act 1991); it is an offence to ride recklessly on a road or in a dangerous, careless or inconsiderate manner, etc.