How to deal with a dead-end job

I'm a passionate programmer in a well-paid dead-end software job. The downside is that I am patching crap code (this week I made several hundred changes much like a human script), and for various reasons I can't quit. The upside is that they are paying me fairly well and I only need to work about 6 (real) hours per day, maybe even 4.

My dream is to work in a more interesting job. Startup, game company, Google, whatever. I am willing to work hard for it.

My question is: How do I keep my head above water and eventually transition into something I would enjoy doing?

More problems: I'm a .NET programmer - people do interesting stuff avoid .NET like plague. And I have to stay in Canada for legal reasons (US is not an option). I am 35 years old, but in the last 5 years or so I did mostly business software.