China is bluffing.  If they had another option, they already would have done it, and it makes no sense for them to wait for Geitner's reaction to their "advice" if such an option were already available.  There are limits to how many US demoninated IOUs (aka dollars) can be converted to euros, yen or anything else, and vice versa, without devaluing China's claims to foreign wealth more than just holding a US government denominated debt.  It is likely that China has already been testing those limits through standard portfolio diversification for the last few years.  

There is also China's more immediate problem that its foreign reserve growth of all kinds has slowed drastically as exports have dried up due to the recession.  It won't buy as debt of any kind, particularly long-term debt, because it doesn't have as much income from trade any more.