Hmm. I personally couldn't, but that is GENIUS! I love it! Get a Bukkit plugin-maker to script that.
A tag on idea... When the bitcoin is mined, it releases a security key, allowing the map owner to reward players with real bitcoins. If anyone gets this working, let me know!
Or alternatively, you could store a real bitcoin wallet in a block.
Genius. Each one would have a special value. Would take a long time to mine. Maybe 32 times harder than obsidian. That would be approx. 128 minutes. It might be worth, for example, 15 mBTC. Just an idea.
Actually sounds awesome.