Possible to scale a shapefile or feature class?

I've got a shapefile (or feature class) that originated from a surveyed AutoCAD drawing and I have the combined scale factor for converting to state plane coordinates. I would like to do this ground to grid conversion by modifying the coordinate system, not by editing the geometry, if possible. I know how to modify the false easting/northing by the correct amount to shift the features into position, but I also understand that features collected in ground coordinates also need to be scaled down by a small amount, this is what I'm not sure how to do by modifying the coordinate system.

Anybody know how I can do this, or maybe can point me in the right direction if I'm not exactly going about this the right way?