I can see where there is a problem...
Sponsorship isn't supposed to be all about someone just handing over money. Its supposed to be a 2-way street, where both the sponsor and the sponsoree benefit from a mutual relationship. IE: The company and branding exposure from being associated with said team. A sponsor depends on using its sponsored car as a vehicle and representative of their company. Now, what happens when the owner also signs another associate sponsor that has a conflict of interest? The exclusivity of the person sponsoring the car is one of the key benefits... I don't think you'd see a Miller Lite sticker on Bernsteins' operation. And if you did, wouldn't Budweiser have the right to be upset?
Business is business. You enter into a partnership of any sort, and you now have more people to be concerned with keeping happy than yourself. If you don't want outside input, then fund a team 100% out of your own pocket. Then there isn't anyone that can say anything about it.