You can run ezWalletMenu.js to add a miner. Simply enter in your account name and then your active private key and it'll edit it for you :) If you installed EZSTEEM with default directory settings don't forget to do sudo nodejs ezWallet.js or else it won't be able to write the config file
RE: EZSTEEM 1.2 UPDATE: Transfer Your Mined/Obtained SP in One Step and Configure Your Miners!