Mounting OEM Front License Plate Holder with No Holes

[Another JR]

I live in a two-plate state, so I ordered the front plate holder (free) but did not have the dealer install it because I wanted it to be removable with no holes left in the lower grille plastic. 
 

The parts have been sitting for a few months and I finally got around to figuring how to mount it. The holder has a deep 1x6 inch rectangular recess behind the upper middle that creates a 1x6 surface that almost touches the bumper when the holder is in place. I thought I’d use some of that really strong double stick automotive trim tape (two layers) to hold it on the bumper, with a tight tether holding the lower mounting ears to the grill in case the tape failed so I don’t lose the plate and holder.  Unfortunately, the tape didn’t stick well to the smooth plastic.  
 

After thinking about it a bit, I thought of filling the recess with bar magnets. Worked great!  I still did the tether, but it’s not going anywhere. I have to pull pretty hard to get it off. The mounting ears hold it in the exact position and in fact take the vertical loads. The magnets just have to hold it to the bumper. If I or a future owner want to have no front plate holder, it just pulls off and I untie the safety tether loop. 
 

I can post a picture and show the magnets I used - $6 worth of ceramic magnets from Home Depot - if anyone is interested.