How to add custom mouse-click actions to Safari with modifier keys? In Safari, when you Ctrl-click on an image in any web page, a menu comes up with several options.

I'd like to be able to do a single trackpad click with a modifier key (option or command, for example) on an image, and have just one of the options from the menu be invoked immediately, instead of showing a menu.

I haven't been able to find a way to do this, but maybe I'm missing something.

I have older hardware so multi-touch gestures won't help me much.

I've also tried the Custom Application Keyboard shortcut approach, but my shortcut was not invoked when I tried it. The menu item is 'Save Image to “Downloads”' and I think I've got the quotes right, but I also tried with plain double quotes (not typographic quotes) and that didn't get invoked either.

I'm open minded about using scripting or a third party add on app to do this, just looking for the quickest approach that really works and cuts the workflow to a minimum.
This is not a perfect solution for your needs, but FruitMenu from Unsanity is the only utility I am aware of that will let you customize contextual menus. It costs US $15.00. It is not yet compatible with Lion. You could download a trial version and see if it will be helpful.

Any keyboard macro program such as Keyboard Maestro should be able to achieve what you need. You might briefly see a contextual menu pop up while it is running its macro, but I think you could live with that.