The problem with "Kiss and Fly" is that there really isn't any decent place for people to wait for someone to pick them up, so that makes it a bit less than ideal.
I'd recommend that they wait for you in Terminal 5 and that you call them when you get to Kiss and Fly. They can then make the quick trip on the ATS to K&F.
Or, just pay a couple bucks and park in the INTL short term parking and go in to meet them.