My wife's brother in Japan has had a similar problem but on a larger scale. He bought himself a Ferrari Testarossa. He joined a Ferrari club and when he told the other members about how angry his wife got when he brought home the car, (she did about $20k damage to the side of the car with a few well placed kicks) their unanimous response was "why did you tell her that you bought a Ferrari?"
Maybe you can just lock your new bike up somewhere away from home so she never has to know about it, like the guys in the Ferrari club in Japan.
Will your wife ride a bike if you get her one? My wife decided that I had too many bikes and it just wasn't fair that she didn't have one, so I bought her one. She has ridden it twice in the 6 months since I bought it for her, which is actually about twice as much as I expected.
Look the bright side, if you buy her a bike, you probably won't have to maintain it...
TD