Sorting Migxdb listbox fields in the grid.

I have several listbox fields in my migxdb grid that are populated from a custom table and are editable in the migx grid. Works great.

However, by making the grid item (column) sortable it sorts, but on the item value (i.e. the id of the item 1,2,3,6,8-etc) and not the option label (in this case a category name)
This actually makes perfect sense, but I need to sort by the category name, not the value of the option.

Anyone know how to do this?