Comment 8 for bug 774059

A workaround:

Hi, I got it working using the "Commands" plugin and "DBus" plugin enabled.
I use the following bash script as the command:
1. Go to command plugin in the Compiz config settings manager.
2. In one of the commands, enter this:

dbus-send --print-reply --type=method_call --dest=org.freedesktop.compiz /org/freedesktop/compiz/scale/screen0/initiate_key org.freedesktop.compiz.activate string:'root' int32:`xwininfo -root | grep id: | awk '{ print $4 }'` string:"match" string:$(xprop -id `xprop -root | grep "_NET_ACTIVE_WINDOW(WINDOW)" | awk '{print $5}'` | grep "WM_CLASS" | cut -d\" -f4 | awk '{print "class=" $1 }')

In bindings, bind that command to a screen edge or button or keystroke, as you deem fit.
Voila!! You have the Scale plugin for the same application class

Note: you need Scale, DBus, Commands plugins enabled. You'd also need to install awk if it isn't installed by default.
This works one way and to get out of the scale mode, press Esc or select a window. I'm still to find a complete workaround for returning it back to normal mode by invoking the same command again.