>how do you give an alternative currency real value?

I'd start by looking at how they implemented the Real in Brazil. They managed to convince an entire country to trust and use an, at the time, completely fictitious currency. There's an excellent article about it, which unfortunately I can't find.

The trick was to get people to start thinking of prices in terms of Reals, while continuing to use the original currency. If you can accomplish that, you've given your currency value.