Start collecting autographed sports memorabilia. Go down to Academy and buy a $15 football and sign JJ Watt's name on it and put it in a protective glass case. Tell wifey it's worth 500 but you picked it up for only 250, when you really spent the money banging your favorite provider's brains out. Only use cash. Not only will your so not get mad she'll be happy that you bought something that can be sold later for a profit. You could fill up a whole room with fake shit you bought to launder your hobby money.
Another upside is if she ever divorces you and files to gain possession of your valuable collection you'll get the last laugh knowing it's just a bunch of worthless crap.