I'm with BK on this one. You can drop anywhere except a marked hazard i think.
The thing is - what do you mean by a "viable location" for relief? Remember, you're taking relief for the obstruction, not relief to get a good swing. So, say there's the tee box and wall and that is surrounded by bushes or landscaping trees and it comes to rest by the wall. You may have to drop in the trees to get the nearest point of relief. which would really stink in that case, but you'd be entitled to relief from the obstruction, not the stuff around it too.
Even if the point of relief from the wall means you drop near a cart path and would be standing on the path, you should take relief from the wall, then relief from the path in a separate motion.