I'm fairly certain that it would work just like shares.

At the point a company is first created it's shares have zero value and so it's founders pay no tax when they receive them. The fact that they gain value later has no bearing on that situation.

Of course, creating shares at a later point in a companies life (when they may have value) does have tax implications.

Thus, any coins that were mined before there was any value you shouldn't need to pay tax on.

Actually the current guidelines are pretty clear. Mining is income. When you receive your coins from mining, that's a taxable event. Current value - mining expenses = income. After that any gains or losses are unrealized until you sell, creating another taxable event. Current price - cost basis = capital gains. Since bitcoins were worthless when Nakamoto was mining, he has no tax bill there. No taxes are owed for simply holding the coins. If he sold today, he'd be taxed at the long term capital gains rate of 15% for 100% of what he sold.

EDIT: but of course I'm making the silly mistake of assuming he's an American.