I've tried this by mucking around with "Set Associations", but all I've accomplished there is messing up the default Open action. I've also found a bunch of registry scripts attached to random forum threads, but I'm too nervous to run them.
You can get 'Open With' in the context menu for any file by simply holding the Shift key as you right click.
To get 'Edit' in the context menu you need to edit the registry. Open up regedit and browse to
For me, open with does not appear even for shift. However, Editing the registry as specified in the other answer does work. With one modification:
You need to use the above in cmd to create a key with default type expandable string.
Also, When I screwed up the open command, I had to fix it by deleting:
and all sub keys.