Using multiple columns as primary key [ or key columns] in pulldata()

My fellow ODKians,
Hope everyone is having an amazing week. I am slightly lost in finding a way to use multiple key cols in pulldata. A simple usecase is: Pulling firstname from 'household csv', key columns are: 'member_num' and 'member_id'.
pulldata query would look like" pulldata('household_csv', 'member_key', 'fname', ${ODK_value})
where member_key = member_num and member_id.

However, this is not possible in given constraints for pulldata from xlsform or odk official documentation.
Is there a logical reason why is it not possible for pulldata to have primary key consisting of multiple column?

Any feedback appreciated.