Sorting an exposed noderefence filter based on another field in the referenced node and excluding unused values?

Couple of questions on exposed filters in views.

I have 2 content types:

Gig, has a nodereference to an artist
Artist, has a textfield called sort

The sort field is used to sort the artists more intelligently than just using the name, so I can sort by the last names of people and remove the 'the' from the start of groups.

So I have a view of gigs, and one of the exposed filters is set to the artist nodereference. This produces a dropdown containing all the artist nodes sorted by their title.

A) Is there any easy way to sort the dropdown by the sort field instead of the title?

B) Is it possible to exclude any artists that do not currently have a gig displayed in the view?

Both are I believe possible by shoving a custom SQL query somewhere in the theme layer when drawing the form, but I would like a more elegant way.

-Ralph Sleigh