Well you must be the first person then i flew the same route and was asked for paper work at all airports and hotels and i'm still here and still getting asked via printoffs
I'm in Pattaya. I used an agency here. But i'm sure their will be an agency in BKK that will do for you. But be careful some will want to charge crazy money i got quoted 8,000 bht found one for 5,000bht so shop around