My cousin is getting married this Saturday at my former Catholic parish. Though I left religion, I still study it objectively. While I will be at the Mass, I won't be participating in it. Rather, I will be observing closely and taking mental notes.
I don't have a problem in participating in the rituals, although I've never taken part in a Christian mass and suppose I might draw the line there. But in terms of being present, I usually enjoy the singing and the atmosphere in Churches, though I'm less enamoured of the sermons.
Being in a Church and being respectful to do some rituals does not change who you are. In respect for friends I have attended funerals and sang a hymn or two, and bowed my head and took advantage of the free time to think what groceries I should buy for the week. Having a drink of magic Jesus blood is not required I'm sure at this wedding event. But if so, just say you can't because you are fasting for Ramadan.
You know the routine, you will be probably more seriously aware then those who go every week. Just smile and it will all be over before you know it. They cannot read your mind but your pretty much into what they are thinking. I would advise to study it subjectively as their is much to learn from the Lutherans, Methodists and others. I was in Israel for six weeks and went to Mosques, Temples, various churches for other reasons. Nothing can compare to the Cathedrals of Europe which are Museums in themselves which took a century or more to complete and we don't know who the artists were. Spain is another out of mind experience and you get tour guides who are not religious but historically as accurate as they know how to be. Enjoy your cousins wedding and you don't have to tell them anything.