Patrick
When you say a "non switchport mode" presumably you mean a routed port ie.
int gi1/0
no switchport
ip address x.x.x.x x.x.x.x
If so then yes as far as i know you can do this on a 6500 as it is just like any other L3 port.
On a 4500 no you can't because the 4500 doesn't support NAT.
Jon