I'm the developer of PopClip, and I found this thread whilst was looking to make this very extension too. (I have had several requests for it from users.) Whilst the AppleScript above would work, it is dependent on the user's hotkey settings, and it is a little clunky in operation. What I would need is the ability to use an AppleScript something like this:
tell application "Alfred"
appear with text "Some example text"
The whole idea is to be able to activate Alfred via PopClip using the mouse only, without needing to press the hotkey. Here is an animated GIF example of how the PopClip integration would work (I built this one using the System Events applescript): (FYI - More about PopClip Extensions)