This was possible using SafariStand for a long time already. This is now a plugin and not an InputManager (which is layed on unstable ground (as Apple wants to

This was possible using SafariStand for a long time already. This is now a plugin and not an InputManager (which is layed on unstable ground (as Apple wants to disable them in the next OS X version)). The killer feature (and what sets it apart from SafariStand) actually is the whitelist. Option-click a Flash object and you can tell it to always load all flash on the current domain. Sweet!