i've seen a few on patrols and cruisers, saw one on a cruiser yesterday actually. just the receiver without a gooseneck in it, but it was mounted to the driver's side of the chassis rail just below the bullbar. there would be nothing stopping you welding some plate steel, probably 6mm min, to the top of a receiver and mounting it off the chassis rail to one side, the only problem is as above loss of approach angle.
i don't know if there would be a way to mount it easily so you could remove it when you didn't need to use it though, but for a permanent mount you could just get longer bolts for the bullbar mount and bolt it through there...