Drat...  I should have wrote and sent  in an article.  But I'm no writer. 

I came up with the same idea  several month ago on my test layout. Posted a pic in MRR. 

I purchased the same magnets for a song.  Only difference is mine are hidden out of view and sitting on an intensifier plate.

Works quite well for the size.   I placed a clear acetate over the magnets to keep balast out.

 You can see one of the magnets in the lower right corner of this picture.   

I never bothered to balast the test track but I did paint it.  Practive with the air brush.

Marc