Continual cleaning out will stress him and could make it worse. Sometimes a minor change can stop the behaviour as it makes them change their habits.
I would suggest a new house, in the same place as the old one. Do you have a photo of your set up? They do best with a house that is open underneath and sat on top of the substrate - they like to bury their hoards under the nest and cosy down a bit.
If you put a larger house in, it can help. Something the size of a shoe box is good and you can then put the litter tray inside the house. That has always worked for me
