I need to filter a built-in NetSuite Customer list/record field on the case form. I have over 100,000 customer records which have a partner field set on them. I want to filter the customer list to only show customers for a specific partner. I don't have access to NetSuite's built-in list/record fields which would be so good if we could (something similar to the way we can filter items on a transaction according to a saved search).

The only workaround I am aware of is to put my own customer list/record on the case and filter it while hiding the real customer list/record field and setting it by script. Problem I'm seeing here is when I select the 'list' menu on the field of the real built-in customer list, the list of records loads almost instantly, while the filtered custom customer list field takes minutes to load and display the list.