You mentioned you've never seen him dance, but that doesn't mean he doesn't know how! A lot of men have trouble expressing emotion, but that doesn't mean they don't love you! May-be he really wants to share in this old-fashioned tradition with you, but is too reserved to talk about it. Would it be too uncomfortable for you to bring up the topic with him? May-be you can make a joke out of it and suggest you do some funky breakdance (yeah, showing my age) to break the ice and then segue into a convo about dancing with you at the wedding. If there's other stuff going on and you just don't want to dance with him, period, then it's going to put everyone in an awkward position because FI wants to dance with his mom. THis one is a tough one. WIsh I had better advice for you.