How do I interact with selected NPC without clicking?

Solution 1:

It doesn't seem a player is able to interact with a NPC via a macro. However, one can interact with a NPC via a built in key binding.

Set up key binding to interact with target:

• Open up the Game Menu
• Select Key Bindings
• Scroll though the list to Interact With Target under the Targeting Functions heading
• Click Not Bound
• Enter the key you want it bind to (example F6)
• Click OKAY

Test It: Select an NPC and push the key you set as the binding key.

Update: Little over a week after this answer was posted, AOL's WoW Insider release an article about this subject. Here is a link to WoW Insider's "Interact with target keybind gets you past players atop NPCs."