When you say ADP require an IR to take a/c away that can't be right as I flew with them last year and though I hold a UK IR this is not valid in the US without doing a written exam. I think they will be happy to hire an a/c especially if you are planning a long trip and many hours. check out
www.private2atp.com
This web site has a database of all schools in the US and can find you the cheapest flight time all you need to input is the zip code
Good luck
