I'm with Nibbler on this one. A fixed angled blade attached with a couple of clamps onto the auger housing is what I'd use.
I'd also use a stout plastic or rubber skirt on the bottom of the blade to reduce jarring if the blade hits a ridge or uneven crack.
Start plowing in the middle and the angle would feed the snow to the sides in each direction. Once it's rounded up, take the plow off and throw it.