lots of care is the obvious answer. If they are the ones off the car i would use a few bits of masking take firstly rubbed on your jumper so its not too sticky .Then put where you think it should go on the car, you could also put a small pencil marks on the paint and mould which will rubb off then check your 1/4 mould to see if its in the same mark then start from that end and palm it on by putting the top edge over the rail and palm the lower side onto the underside just take your time its not that hard.