I.S.
I also lost my mother..five years ago. I totally understand hating the whole "I'm sorry" routine.
But it might help your uncle to just simply be there for him. Provide that support that he needs. Maybe help him to focus on his own emotions by doing small errands or chores that are menial, but necessary (taking out the trash, doing dishes, etc). You can also try asking him how he is doing..or letting him know that if he ever needs you..that you are available.
I wish I had more concrete advice for you, but I think death is one of the most awkward situations we can be put in. Best of luck.