Mike, I knew a guy who would spray the backside of his birds as he pulled them outta the pet carriers after coming home from a show. As I recall it was just a couple 2-3 squirts. If I remember right one of the articles on this thread said the Fipronil is absorbed by the skin AND feathers. Not sure how feathers absorb it but if that's the case then the spray I reckon would work.
FWIW, I don't actually use Frontline but rather the knockoff brand at Walmart. Forget the name, but that doesn't really matter, just look at the percentage of Fipronil and get the same. You'll save 10-20 bucks. I buy the box that has plastic tubes you snip the end off of. Get the dosage for the biggest dogs. It's the same price as the small dogs. I give the birds what amounts to about 3-4 drops about an inch up from the vent. And maybe an additional drop or two at the back of the neck if the infestation is really bad.
And here's a little tidbit that might be helpful. If you have too many birds to do at one time you can pull the wing out and pluck the feathers from the triangular flap of skin on the right or left side and put the drops in there. Then hold the wing shut for a few moments and it's absorbed. Just make sure you use the same wing on all the birds. Then when you come back the next night you can quickly tell if you've treated that bird or not.
As a reminder, I only had to do this once about 10yrs ago after battling the Northern Fowl "Super Mite" for 3yrs., One treatment of Fipronil finallly wiped them all out and I didn't have to treat again. No followup was necessary.