everything is assignable (as far as I know) in V7. the interface is in a different place and is a little different look than before, but I think you can do it.
Just go to options -> Customize Keyboard
then type in the "show commands containing" box "audio" and there you will see about 3 or 4 down the list "Tools.Audio.OpenInAudioEditor" and then you just go to the assign box and type the text that you want, Make sure that you select the right area that you want to do it in (The 8 boxes accross the top that have different names like "track view" etc...)