I wear business casual to a school and work part-time in a department where people sometimes wear black denim jeans instead of dressier pants. I am dressier than many of those working there.
I have occasionally worn black skinnies with a long tunic and tall boots so that there is very little of the jeans showing.
Now that it is warmer weather, I also find myself really keen to wear my denim jacket to and from work (but not while I'm there).
I'd be interested to hear what others thought about these and other similar denim-business-casual situations. I'm very happy to be entirely disapproved of!