Get a Japanese girlfriend.

If that's not possible, sounddust's method seems the most likely for a hacker with limited access to Japanese people.

With Japanese, you risk ending up speaking fluent Japanese-girlfriend, rather than what you would be expected to speak as a Japanese-speaking male.

This is valid, you will sound like a girl. However, it's better than not knowing how to speak at all. It isn't so hard to correct - just go drinking with some old japanese guys once a week.

I can't imagine any possible awkward conversations from speaking Japanese-girlfriend