Actually Phil, as I dont have the ability to interview everyone, so youre asking for evidence you know I can't produce. (a bit like saying 'Well you cant prove there is alien lifeform out in outer space, therefore it can't possibly exist' - ie not being able to prove the negative, doesn't necessarily prove the positive).
However from the list of z-list celebs who have run for charity you have Jade Goody who entered one year and then gave up after 2 miles. You have Lauren Goodger who entered and took up a spot, only to withdraw before the start of the race as it was 'too much like hard work' ..... and you have Arg from Towie who took 6 hours to do the course, roughly the same paces as if you had just walked the whole thing.
So there are 3 examples for you anyway.