Neither do I know a definite answer to Katia's recent question, though for some fifty years I've only ever heard the verse involving the bus and the grannie, until encountering some additions in the last decade (and a few more in the last half-hour...). One of these not included above involved a brother and the same vehicle:

"O Ye cannae shove yr brither aff a bus,
Naw ye cannae shove yr brither aff a bus,
Ye cannae solve yr brither
Fur he's a drunken blether,
Ye cannae shove yr brither aff a bus"F

(A derivation from Burns's "Tam o'Shanter" seems likely for the "drunken blether" part; in Scotland, and no doubt at least some other countries, "blether" can be both verb and noun, singular for a person who blethers and plural for nonsensical chat and politicians' promises). This verse was sung, or declaimed, one New Year on Portobello beach near to Edinburgh, along with some others. It may be amusing, though admittedly unrelated to the immediate subject, to know of a contribution made less than a month later and in the same location, as part of an "Alternative Burns Supper" organised by the Scottish Socialist Party. There had been a few poems and songs made by the man himself, there had been Haggis &c. previously cut up and thus not "addressed", and then this young guy with a guitar steps up to the microphone (aye, there was a P.A. system as well);

"Good tae see yeez at this Burns Supper. Here's a song I just wrote a few days ago..."
(and then went on to sing it! Nae kiddin'!).