I know it's a pain, but it works, and you only need to do it once if you remember to take a copy of the modified building.
For example, the Library on Intersections, based on Amiryu's lovely Matsumoto Castle which was originally built in SL, has lots of stairs and needed ramps on all of them.
To do this I found the base slope prim, unlinked it (carefully!) from the rest of the build, copy-dragged it roughly to the front of the stairs, switched the texture to plain for greater contrast, then linked the prims (VERY carefully) back together in the order ramp--base-slope--structure. Then I isolated the ramp in the structure and made it invisible.