Without making you feel sorry for him or his disability
Most Helpful Girl
Own your state. Don't ignore it and pretend like you're standing.
Don't be afraid to make jokes about yourself. Look confident, include your disability in your self presentation. Say she rejects you, you catch up to her and say: "Is it the chair? You think it makes me look fat."
I'm not saying to make everything you have to say about yourself about the disability, because that too is neurotic and she'll notice. Just relax and if it comes to mind, don't avoid to include it.
When you embrace what is outside without the neurotic need to compensate for it, others will have less of a reason to see you through your disability, because you'll be presenting more of who you are inside.
And I'm not sure how to recognise girls who pity you. I know when people pity, there is that lingering look in their eyes I can't explain. I hate it, so it must suck if you see it a lot. =/0