Like people have said, loosen your shoe laces when you are getting on an elliptical.
Also, if it happens even with that, get off the machine and walk around for a minute or two. Do high knees, and then get back on the machine. Sometimes it is just our posture, and the specific pressure points we are hitting when we stand specific ways. A simple shift, or release, could help.
Don't mind me. I'm an invisible person who everyone forgot. No friends, no support. Nothing. Thanks 3FC for making me realize how invisible I really am!