My wife's ward just changed bishoprics a couple weeks ago.
I wasn't at church but I am friends with all of the new members of the bishopric. I have teased both counselors in a friendly way about how much time their new callings will take up and mentioned that I no longer have to worry about things like that. It got your message across to them pretty well I think, especially based on their good natured, yet resigned responses.
I actually had joked with him a bit that if they called him I would have to oppose due to him not having enough time. He smiled but didn't say anything---so maybe he's already resigned to it or isn't being called.
Perhaps I'll let him know that if it gets to be overwhelming, I have a few questions he could try to answer for me. In finding the answers, he might find a lot of extra free time too. :)
I agree with BC. It would be more appropriate (this in just my opinion) for you to express you concerns as a freind to this young man. You could tell him there will always be another time he can serve as a bishop.
As long as you know that opposing a calling make absolutely zero difference in whether or not the calling goes through.
You opposing a calling will just show the leaders that there is a problem with YOU, because there can't possibly be a problem with THEIR "inspired" decision.
Often they'll stop the meeting and take the dissenter into a side room to discuss the issue. There you could voice your concerns, and your concern may even be appreciated, but they'll most likely go back into the chapel and make him bishop anyway.
Assuming that you don't go to this ward often, it will only make him look bad. If you do go to this ward often, then it will make the two of you look bad... Everyone will think that you have information on him and that you are a snitch. It will embarrass him in front of all of his peers.
If he really is a friend and you really do care about him, talk to him directly. Doing something so public would not help him.
My initial reaction is nonmembers are outside of this organization and should really leave it alone. Then my 'Nam flash backs take me to places in my head where I sat through meetings where bishops, stakes presidents are saying stuff like the bishop can get revelation for every one in their ward, stake what ever boundaries. So, if some guy is thinking he is getting revelation for some one who does not know the organization exists, maybe you should show an unsustaining vote if you live in his so-called jurisdiction.