Oh, wow, I hear you. Here are a few hints:
- stand up and go to the bathroom
- Have a handy empty water bottle and stand up and pick it up and say "Gotta get my steps in, I'll see you soon."
- When you see someone coming, pick up the phone and pretend to dial a number. If they don't get the hint, just mouth "I'll swing by later"
- Look directly at your screen as they talk and then do an "Aww, shoot, hey, I gotta get to this thing. Thi se-mail is just crazy!"
- Write a bunch of notes as they're coming into the office and then just say "I"m sorry, I have to get these talking poitns out soon"
- Make sure to keep any random chairs full of papers or whatever.