first, you need a 'start-many' config that uses the 'masternode.conf' file
then, to the end of your masternode.conf line (right after the output index integer) add: destinationaddress:percentage
e.g. <alias> <mnaddr> <mnprivkey> <txid> <vout> Xblahblahblahblah:10
to send, on average, one out...