Cat Messing in the House

[Bushbaby]

As most of you are aware, we have a three-legged, vegetarian cat (don't ask). Recently he has taken to doing no 2's in the house. At first it was just around his litter box when it was full (he is a busy chappie) but now, even when the box is cleaned out he is messing around it rather than in it.

We have bleached the floor thoroughly to remove any trace of smell but he is persisting with this bad habit.

Does anyone have any suggestions on how to break this cycle of bad behaviour?