Lookup Sort Order with Hidden Field

Lookup Sort Order with Hidden Field

I have a multi-select lookup list called "Categories".  Within Categories, I have two fields - a "Category" (string) field, and a "Sort Number" (decimal) field.  The purpose of the Sort Number field is to manually allow the user/admin to re-arrange the Categories on display/print.

I would like to display the Category field of Categories as a multi-select, checkboxes lookup in the order of the Sort Number for each Category, but I do not want to display the Sort Number.  How do I do that?