As Cheshire Figment and Talking Hands have said, the easiest way is to ignore the finger scanner and go straight to a gate between turnstyles. You will however need a picture ID with you, like a drivers licence. Because my UK driver's licence has no picture I just show them my London bus pass which *does* have a photo.
My first few years with an AP, I did use the finger scanner, but it often failed because I had to squirm around at an odd angle to fet my fingers into the scanner from an odd angle sitting in my wheelchair so that my fingers were not centred properly.
Last trip, I just ignored the finger scanner altogether, with no problems.
One thing to check though - dont let the CM at the turnstyle forget to put your pass through the machine (as one inexperienced CM did for me). You cannot get fastpasses with your AP, if the AP isn't registered properly as you enter.
Andrew