Sorry, it's been brought to my attention that I should mention you could do this by creating a sym link.
You'll need to do this from the command line. The command is "ln -s [source] [destination]"
1 - Move the clippings file to where you want it to be located
2 - Open the Terminal.app in Applications/Utilities
3 - In Finder, navigate to the <home>/Library/Application Support/OmniOutliner 3/ folder
4 - Drag the Clippings folder to the Terminal window and push return
5 - Type in "ln -s" don't push return yet
6 - Drag the clippings file from the Finder into the Terminal window
7 - Type in the full name of the clippings file, the default would be "Default Clippings.oo3" if there are spaces in the name, put quotes around the whole name
8 - Now push return
You should now have what looks just like an alias file in the Clippings folder in Finder and you should be good to go now.
Let me know if you run into any trouble with this.