Make your breakable wall. Give it a targetname.
Make a func_static brush the same size as the breakable area, and very thin, and right infront of it. Cover it with clip so the player cant see it. Click 'use_push' or something like that (press N, and there should be a few options) click the force push one, or pull... then tell the func_static to use a script. Give the func_static a targetname also. In the script, say "use" then the breakable wall targetname. After the use line, put remove then the func_static targetname... and thats it.