Independent of being a real estate broker, I think I may be more useful to you from the perspective of being a small business owner in Minneapolis. I also spoke with the person I referred to in my prior response. He is willing to sell and offered to provide insight if you wish to call him. You may contact me @ #612-822-1771.
Be prepared to explain why you must 'own' a duplex. Is it necessary to own the duplex in order to conduct your business? Why not rent a duplex?
If it's imperative that you must own:
Interviewing reliable small business accountants and small business lending experts, whether local bank or broker, is essential. Maybe you've already exhausted those routes? If so, you will be limited to private financing or some creative means.
Whatever you do in the realm of property and/or start-up small business business ownership, expect to offer personal guarantees based on credit history, financial statements, collateral/ assets... That's what most of us business owners subject ourselves to in order to borrow or lease, especially when starting from scratch (high risk).
I have a past client who owns and uses a Minneapolis duplex in the same fashion you've described.
He lives in and occupies the upper level as a residence, the business he owns has operated as occupant of the lower level. Also consider this is an established business with 5 or 6 employees. In the past he co-owned the building with a business partner, although I am aware that he recently bought out her stake in both the duplex and business (and possibly refinanced).
Nevertheless, I trust he has explored every angle you're considering with respect to how to go about financing, tax implications... Please let me know if you'd like me to learn more or make the connection. Maybe you can buy his duplex?