The BMW factory navi system doesn't use the controls on the steering wheel. I think the steering wheel controls are just redundant inputs for the bezel controls they represent. Since none of those redundant inputs is used by the navi system, they don't affect it.
Installing a BMW factory unit in a vehicle without navi is ridiculously expensive and not worth it, although it would look the best (are you so rich that money is no object?).
If you are talking about an aftermarket one, I think they exist that fit in, but there may be nightmarish wiring issues that you might not want to mess with. Someone on this board went thru that nightmare (myharley).
If it was me, I would buy a good quality (large database capable) portable unit and mount it and use it that way.