Map it using the vpp should work. Tried custom route?
Check out example for custom route here at the bottom
For older sites I used this approach with virtual path mappings to override EPiServer default pages.
Don't customomize the actual logout.aspx however. To tricky to upgrade then :)
How can i customize the EPIServer editor logout to my customized route (URL). Bascially i want to change the /util/logout.aspx to different route.