Just got back from the NSRA Street Rod Nationals. Could not wait to play with this. I used an old worn out "bondo spreader" which was a little too transparent. I added 3 layers of masking tape and shaded it with a pencil and then one last layer of masking tape. I had not seen the last few posts or I might have gone with SafeAirOnes's method but this truly worked great also.
Here are some pictures of what I did with excellent results.