I don't know how to transfer, but I was just accepted to GSPIA for the MPIA program. I am just out of undergrad, gpa: 3.75, GRE: Q 710 V 680 AW 4.5, pretty good recommendations (but all from my Philosophy professors... my major in undergrad), and I came from Texas A&M U, which is a decent school. I also had minimal international experience: one month Spanish immersion in Costa Rica, and a few short trips. Anyway, hope my profile helps. I got accepted there, and a few other more competitive schools, but I am waiting on funding info for Pitt.
I have to say, I think starting an MPA program would just be throwing money away if you are planning on an IA degree. You really don't take the same classes, so I'm not sure what you would be able to transfer, even if it were possible. I would try to apply for Spring admission (I think Pitt offers this). There is a plus: oftentimes Spring admissions are less competitive!