Have you tried having a box in each room he visits? That may make it easier on you having to move it all the time. If he was a feral kitty or born outside to a mom who would have trained him to go wherever it probably will take a little longer.
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!