How to add custom mouse-click actions to Safari with modifier keys?
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.