I think there is only 1 way to perfectly implement this pegged value idea. Create a DAC (Distributed Autonomous Community) whose sole function is to take an amount of BTC as an input and return the same amount of XBTC to you in return. This DAC will run on at least all the underwriters computers. This keeps it as simple as possible. The DAC is trust-less and starts with the 21 Million XBTC. To get the XBTC you have to feed it with BTC. All the accounts would be transparent and really simple - only 1 address is needed for both the BTC and XCP.

This would work for any other crypto-currency too. The only caveat being that the members of the DAC community would have to run the blockchains of each cryptocurrency involved.