Plausible suggestion, Wm., except that Melville places "Booble Alley" in Liverpool.

OTOH, the British newspaper database produces only three refs. to London's Blue-bell Alley from 1780 to 1856. Where it went to after that I don't know.

If Blue-bell Alley was so unworthy of mention, Booble might have been as well.

I couldn't find a "Gibraltar Place" in Liverpool, either. Or a "Rotten Row."

Or a possible "Bauble" or a "Bubble" Alley.

"Buble" is a very rare English surname, known in the 19th century mainly in Warwickshire.

So possibly "Buble's Alley" was named (temporarily) for somebody who lived there.

Well, possibly.