unless I misunderstood,
you just go into the EDITOR CONTROL dialog,
and under the ROUTE tab
click LAYER SETTINGS
and then clear the checkboxes for everything except your surface layers
Thanks. That makes sense.
Also you can control which layers to permit routing using CES. That way you can control them by Net Class. In addition, find the Layers column in the AutoRoute dialog. There you can control layer usage by Pass Type.
Get in touch w/me if you want to go over this a little more.