Don't have my books in front of me, but here's my two cents worth.
I would treat the unconsious victim as unable to "dodge" or move out of the way, in other words, an unattended object is the closest thing that comes to mind.
Unattended objects do get saving throws - so an unconcious victim should be allowed one as well. As for the dexterity, evasion, improved evasion, I would not allow the modifiers to come into play. It can be argued both ways, "He's unable to move so apply a -5 modifier" If you allow the -5 modifer, one could argue that an 18 dexterity does come into play (Thus the +4 modifier).
LT