Here is an article on 'Wizard' as English slang. But no origin. I've never heard anyone say it, but only come across it in British children's papers and books.
Interesting article.
I only remember hearing it used in a sketch of the Dave Allen At Large show (I tried to find just the sketch on YouTube, but if it's there it's probably as part of a full episode).
IIRC the sketch has a man rub a lamp and a Genie appears. He says, "Wizard!" and a wizard appears. He says, "Golly!" and a golly* appears. He says, "Devil take me!" and the devil appears and takes him away.
* This is probably the reason why the sketch itself can't be found on YouTube, the blackface appearance of the golly.