Jason,
try putting a litterbox where ever he is choosing to go at night.  My
ferrets on occasion seem to tire of certain spots and start somewhere else.
I have learned to move litter boxes to where they are going and they will
then use those.  Also if it is somewhere you really want to discourage, try
putting a bowl of his food there or some old towels (bedding stuff) because
most ferrets wont "go" near something they perceive as a food or sleeping
area.  Usually this will help significantly.
 
Good Luck,
Karla
Meep and Daisy
[Posted in FML issue 2330]