How can I (F31) help my friend (M31) feel included even when he’s refused to take part?

Hi all. Weird question I know, but I’m going to give context.

I (F31) and my friend group are all having a Christmas meal together in a couple of weeks. We’re all in our early thirties and are made up of several couples, most of us have known each other since we were kids.

One of my friends who I’ll call Nigel (M31) started seeing a woman (F32) early this year and they have become very serious- we’ve rarely seen him this year because he’s spending all his time with her and we’ve also only met her two or three times. She’s perfectly nice, but shy. Nigel has always suffered with his mental health, and we get the idea she’s probably similar. Of course the two of them were invited to the Christmas meal.

We also all decided to do a secret Santa in the group, and exchange gifts at the dinner. Since Nigel has been super quiet in the group chat this year, I didn’t want him to miss the memo about the secret Santa so I messaged him asking about it.

He told me that they will come to the dinner but they don’t want to be involved with the Secret Santa as the idea of finding a good gift for someone makes them both feel anxious. I said that was fine, even though now I feel awkward about the fact they will be the only ones not receiving anything from anyone else at the dinner.

I’ve got my own secret Santa person, but I was thinking I could get Nigel and his girlfriend a small gift each too without making it clear who it’s from, so they at least have something to do while we’re opening gifts so they’re not just sitting there awkwardly, and potentially feeling crappy at being left out. But then I wondered if secretly getting them a gift would make them feel bad because they don’t know about it and can’t reciprocate, even though they’ve chosen not to take part.

Sorry for the rambling, I hope I’ve put across what I mean clearly. Why would it be wrong if I got them gifts even though they didn’t want to take part in the secret Santa?