Many, many people know the correct meaning of these two words. And many, many people have heard him mis-speak, and have chosen to say nothing - including his boss, his peers, his family, and so on.

If all those people have chosen to say nothing, leave it alone.

If this was a subordinate, or your spouse, you wouldn't even ask the question, you'd just correct them quietly one day.

Your boss didn't hire you to be his grammarian. Focus on the things that are really important to the business, and let this one go.

I think it depends largely on the kind of relationship they have. I could quietly point out a mispronunciation to my boss and she wouldn't give it a second thought. I personally would appreciate being told. I once had a co-worker who used to constantly describe an angry person as "fumigating". Since I was pretty sure he meant "fuming", I occasionally worked the correct word into conversation in front of him. After a little while he made the switch to fuming, and no toes were stepped on.

Just get him one of those "word of the day" calendars where the words are obviously wrong (at least to you). There was an episode on "Just Shoot Me" where they did that for/to Nina.

If he actually uses these words as given, he will likely get fired and then you can have his job.