Contour Lines through buildings?

I have an .las file that has buildings and ground.  After classifying the points, I create an elevation grid filtering out pretty much everything except the ground.  This leaves me with a pretty good picture without any of the buildings in it. then I export it to a .dem file, so I can get the contours.  
The problem is I want to see the contours without the building interfering with them, right now you can still see the outline of the builiding with the contours.  Is there any way to get rid of the building interference without just deleting them?

Thanks
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