Palm,
I'm in the same situation as FFIL; waiting for surgery and frustrated, depressed, embarrassed by my looks. I force myself to go out with my friends and I'm glad I do because it helps lift my spirits. My suggestion to you would be to make them part of the planning process as much as you can. Give the FIL's something to do; phone calls; having a voice in picking your menu, your flowers, your invitations, etc. I know that being an active part in my family helps keep my mind off what I have to face. It's not easy for him to put this out of his mind but the more often he can get his mind off it the better he'll feel about it. I'm invited to a wedding in July and I probably won't attend because of how I look. People are supposed to be looking at the bride, not the freak side show! I use a peg tube to eat so what does one do at the dinner table while everyone else is eating a wonderful meal? I think if you give him enough to do to make him feel he is participating in your special day, it will be enough for him. Maybe he'd be comfortable sitting in the back of the church after everyone is down the isle. Perhaps you can plan to stop off to see them for an afternoon tea before the reception. There are lots of possibilities to make them feel a real part of your day without having to be there. Talk to your FMIL for ideas; she might know what he'd like. If I think of anything else, I'll let you know.
Pat C