I do something similar to GW, on the mizzen...but...
I have fitted a burgee bracket, screwed to the mast, and have a racing type burgee, to which i have glued appropriately sized miniature union jacks (ebay, £5ish for two) so as to make a Small ensign, which also works as a proper burgee.
Sorry not the best photo!
Conventional, aft deck/rail mount staffs are problematic with a boomed mizzen sail.