I have just fitted a MGF Trophy front splitter to our F - I used 6mm double sided foam tape from ebay along the top edge, self tappers on the wheel arch and cable ties underneath - road tested it for 2.25 k miles through eurpoe including near 30' in Italy, low tempretures in the Alps (still snow on the ground), heavy heavy rain in Germany and a bit of 3 figure speeds, also in Germany - I can confirm that the tape works well.
And that the splitter improves high speed stability.
Something like this -