Your screen will dim automatically after the timeout period.
It would be easy to lock the screen with a DBus call, but IDK if opening the application and then locking the screen would be annoying.
I suppose it would work ok if you had the auto-start option on.

Quite a lot of those things are possible with hacky workarounds I think Copernicus would like to avoid stuff like that. Things like that were tested in earlier versions and removed/commented out

Camera Lens Launcher
http://maemo.org/packages/view/cl-launcher/
With the current features of Lanterne the two applications work well.