Loading joined fields in a saved search to a sublist

I have a sublist on a suitelet, and am loading the results form a saved search into it. All good, except I have not found out how to load the joined column:


i.e.
columns[columns.length] = new nlobjSearchColumn('custentity_bank_account_name','vendor',null);

into the sublist:
sublist.addField('custentity_abagen_bank_account_name','text','Vendor Account Name');

any ideas, greatly appreciated!

Thanks