For those who need it, these are the lines to add to your gridcoinresearch.conf file:
enablesidestaking=1
sidestake=bTNdoTqkFAmdSHz3MYEkqLgjCCmFFJUAmn,PERCENT
Note that PERCENT is a whole number representing the value of the percentage. For instance if you wanted to side stake 25% you would enter "25" for PERCENT.