Near the start of this thread Snuffy mentioned a snippet from a book:

"And finally, our Wellerism probably shows contamination with another and quite unrelated Wellerism, "'Aha,' she cried and waved her wooden leg. ... "

The rest of the book doesn't further discuss this line, but it is quoted in discussion of the line:

"I see, said the blind man with a shake of his wooden leg, that the price of lumber has gone up."

Suggesting that this is an earlier version, and that the "Aha" is a derivative.

There is also some mention that the blind man referred to comes from a line of italian origin, but there are multiple references to blind men apart from this one.