Is that still the insertSelectOptions call?

It's

Field.addSelectOption()

... If you need to fill it out later after the sublist and field is defined, use form.getSublist(), then use sublist.getField().

Thanks, that’s exactly what I was looking for. I have another situation where the user enters a field and then I wanted to source a transaction field with just the values related to a customer. Is that going to have to be client?

Yeah, in that case I think you would have to use

insertSelectOptions

of the search result since you do not have access to serverWidget module on the client script.