The only way is to use prop_dynamic's with wall models
But, may be there is another way:
http://www.youtube.com/watch?v=mjGByP5hRNY 1.05
There is a transparent bridge which is made of brush and players can spray decals on it. Perhaps you can recreate this brush entity with the help of this tutorial and texture it with decals
When the bridge disables, decals sprayed on it disables too. So, even if it will work, you won't be able to make physics visible brush this way