I applied from Germany. You will obviously have to go to the schools for the interviews, but most secondaries can be done from abroad (i.e. download and print out the secondary, then mail it). However, it helps if you have a US contact person (parent or family member) who can forward you the hard copy secondaries.
You'll probably want to put your US address as your mailing and contact address or else schools may consider you a foreign applicant, but I'm not sure how that works.
Anyway, the process can work from abroad, but be prepared to pay a lot of money on postage! : )
Good luck...