In all honesty, I would do something sentimental this year. It is his first year with out his wife, it is going to be hard, no matter what. He wants to know that everyone is thinking of her and is not forgetting her. He wants her to be remembered and honored. This is one thing we are doing for my mom (her mom passed away last year) - we (her children, their spouses, and the grandchildren) are making a "Love Jar". There is 52 notes in it. Once a week, every Sunday, she is to pull out a love note. We have all written happy memories we have of Grandma. We did this previously, but wrote all the notes to our mom, happy memories we have of her. She has said it is her all time favorite gift and it cost us nothing to make. You could do it either way, everyone writes memories of MIL on the notes, or everyone writes memories of times with FIL. Even being male, I am sure he would love it. :)
My other suggestion is, if people can afford it, take a winter getaway. Go somewhere warm together, or go to a winter cabin together. Spend time together, talk about MIL, enjoy each other. My thought is that this year is the year to do the sentimental stuff, as he is going to be thinking of her more this year than any other.
Good luck, let us know what you do.
S.