If you go to their main webpage and look for join you then can create an account. IIRC the 1st block is where the code goes. I don't think you can use BOINC to create the account.
hmmm when I go to their home page I don't find a place to join. the only thing I find is instructions to download boinc and to use add project. it hen tells me that they are not accepting new accounts.