Curse, swear, spit and foam at the mouth as you fill them with bondo six or seven times and it still isn't flush. Then eventually you get it right (at least that is my hope)
Actually what I did was plastic weld the inside then use bondo on the outside - it has been a tad laborious but now they are all but invisible.
If, however, you choose to go the flag route as suggested by Laitch I have found Union Jacks tend to make policeman salute and barriers raise as if by magic....
