Single select list from custom user field

I added a custom field to the user list for users that can give exceptional approval for a process and want to show the list of those users by a single select widget, how can I do so ?

I know how to make a query on a table and than add an aggregation but that can be done only on a Tulip table, I also know how to make a connection function to filter table by field’s values but that is also only on a Tulip Table.

So, how can I filter and select banch of data from user’s table ?

Thank you,
Happy Hanuka and Merry Christmas,
Amit Berku