The method uses AppleScript and the code is super simple:
tell application "PopClip" to appear
The documentation suggests using a few third-party “launcher” utility apps, but I’ve discovered a way to do so with just OS X, using Automator and OS X Services. Here’s how I did it.
First, you need to launch Automator on your Mac and choose “Service” for a new document. Drag the “Run AppleScript” action from the list over to the right side. Using the AppleScript above, configure the contents of that action as so (note the ‘no input’ selected for ‘Service receives:’):
Save the file (I named mine “PopClip – invoke”).
Next, go to the System Preferences and click the Keyboard prefs, and then the Keyboard Shortcuts tab. On the left-hand list, choose Services, and scroll down to the Text section to find your newly-created Service:
Note in the screenshot that the arrow points to the custom keyboard shortcut I assigned. You’ll need to manually do the same by clicking the gray “none” text, which will reveal an “add shortcut” button. Click that button to add the shortcut of your choice. As you can see, I chose Control-X for mine.
You may need to quit and restart open applications for the changes to take effect in each app’s Services menu.
Now you can highlight text using the keyboard, then type the Control-X combo and PopClip’s menu will appear. You can navigate the menu options with the left/right arrow keys. And because we made sure the Service had ‘no input’ chosen, you can invoke PopClip without any text selected (for pasting), but still works fine when text is selected.