I can empathize with your problem. You don't want to make a big deal and you don't want to offend or embarrass your friend, you just want it to stop.
What it boils down to is how much does it bother you. It seems most likely that dealing with the situation in any manner will involve at least some level of uncomfortable confrontation.
Being an adult and politely asking him to scale back his rather obvious fudging doesn't guarantee that he is going to be an adult about it. And that is the op main worry. It seems to satisfy yourself you are going to have at least some level of discomfort by bringing it up in some fashion
The least confrontational approach would probably be a polite blanket statement that a little too much fudging is going on and while some isn't bad, repetitive fudging can take the fun out for others.
As I've gamed with same people for years I can understand the awkwardness of confronting a longtime friend with fudging his rolls. It seems that if you're going to get some satisfaction you are going to have go outside your comfort zone.