In case anyone else runs into this problem, here is the response I got from Mortgagebot:
"You are correct, we cannot configure disclosure display based on 1st lien Home equity and second lien home equity applications. You may want to consider always presenting this disclosure for all of your HELOCs but with language identifying that the information is only when the HELOC is in first lien position."
I will present it to our compliance department to see if they are comfortable with this option.