1. Backing Bitcoin would require a central authority and being decentralized is one of the key characterisitcs of Bitcoin. Without decentralization Bitcoin would loose value, not gain it.
2. If you still think its a good idea, you can go and start goldcoins, silvercoins, ricecoins or dollarcoins. Let the market decide which one it prefers. But I would take a good look at what happened to Liberty Dollars.
I think it would be a great idea to start something like goldcoins, that keeps their value stable against gold. It wouldn't be necessary to have any physical backing or central authority to do this.
Let me suggest a very crude way to do this:
Instead of having a predefined rate of growth in the number of coins, the difficulty of mining coins could depend on the exchange rate between goldcoins and gold. So let's say we set the target exchange rate at 1 gold coin for 1 gold gram. When the price of goldcoins rises above 1 gram mining becomes easier, increasing the supply of goldcoins until the price comes back down to the parity level. When the price of goldcoins are at 1 gram of gold or lower, mining new coins should be virtually impossible so that no new coins are mined until demand picks up.
Whenever the price falls below parity speculators could make a profit by hoarding goldcoins at the reduced price and then selling them again when the price comes back up. This would increase the demand for goldcoins and drive the price back up to the parity level.
This should basically be enough to keep the value of goldcoins stable against gold. I do also have some ideas that I am working on about how to make the mechanisms for keeping the value stable more efficient and less likely to fail.