Can I set Lion scrollbars to always be off? (Except when a mouse is plugged in)

I like the fact that scrollbars disappear in Lion, but only if I don't have an external mouse plugged in to my MacBook Pro. Is there a way to have this behavior always be on?

I know I can set the vanishing scrollbars to be "always off", but I'm basically looking for a way to do the opposite.

Asked in other way: I know we can set the scrollbars to be Always On in the System Preferences, but looking for a way to do it Automatically NOT based on input device. I don't want to see a scroll bar unless/until a mouse is present on the system.

The option you mention in System Preferences does exactly what you say (or its behavior was changed since your question).

The first option, "Automatically based on input device" does what you want (I think, but I may have misunderstood your question). When you have a mouse plugged in, it shows the scrollbars. When you unplug your mouse, it will revert to the default of only showing scrollbars when you are scrolling.

I hope this answered your question. Please let me know if it doesn't, as I probably misunderstood what you are asking.

I don't think there's a specific setting for what you're after, but you could use an application like ControlPlane (formerly MarcoPolo) or Sidekick (there's other alternatives too if you are keen to keep looking).

These let you set up different profiles for using your computer in different places or contexts. Typical usage is to detect what location/context based on some inputs (e.g. wireless networks, bonjour hosts on the network, peripherals plugged in) and automatically switch to the appropriate profile (or just let you manually do it).

Profiles can include things like Network Location, turning on/off Time Machine, changing some system settings, and running various scripts.

So for your situation, you'd potentially just have two profiles: Mouse and Trackpad. The presence/lack of your mouse could be detected to allow automatic switching, and you'd have to set up some rule(s) to change the System Settings as required.

The appropriate command-line to change your scrollbar viewing would be:

defaults write -g AppleShowScrollBars Automatic

For that last value, you can choose between Automatic, WhenScrolling and Always (i.e. the three options presented in System Preferences) — thanks to this answer for the tip.

I won't go into too much detail as there's plenty of other places that document the various System Preferences and modification of those via defaults write (you can use defaults read to see various settings for yourself too). So it's then just a matter of coming up with the specific commands to run as you switch between your Mouse and Trackpad contexts.

(If you've already got different contexts, you might need to duplicate them, e.g. "At Work with Mouse" vs "At Work with Trackpad" and set them up similarly but with the command to enable/disable scroll bars on switching to said context).