Try laying it on the top of the dash or even attach it to your passengers sun visor with elastic bands and fold it down so you can se it through the windscreen.
Job done, one secure number plate that won't rattle/slide about your dash
But then won't your sun strip block it?
It needs to be up against the window so speed cameras would be able to get the reg otherwise mr officer has a reason to pull you.
Going back to the original question, why not just buy some sticky pads and put it where the bumpstrips used to be for a week or two? They come off easy enough afterwards with a bit of white spirit.
i got put on a register and told i have a week to stick it on the bumper or ill get a fine, so i did
^ Vinyl sticker reg plate FTW.
I reckon your best bet is sticky pads if you don't want to risk it matey. Get the bigger spongey ones as the rounded Clio bumper does not take kindly to the thinner ones!
myns