This is a bit tricky currently. It involves copying the file into the installation area. The Mac makes this especially difficult, and there are 2 different sets of instructions, depending on whether you're using the AppStore installation, or the one installed from autodesk.com.
First, put the file in your home directory, or some other location where you can find it -- you may need to repeat the below again if an update is pushed.
On the Mac -- for an autodesk.com installation -- the installation area is as follows:
~/Library/Application Support/Autodesk/webdeploy/production/<someGuid>
"<someGuid>" will change for each major update. The most recent update uses a Guid starting with "6fcf".
The CAM post processors are stored a few directories down, so, the directory for the post processors is:
~/Library/Application Support/Autodesk/webdeploy/production/<someGuid>/Libraries/Applications/CAM360/Data/Posts
The easiest way to get here is to just type the text before the "<someGuid>" into the "Go to folder" dialog in the Finder, and then navigate down from there.
Once you get to the Posts folder, you can COPY your .cps file into that folder.
After restarting Fusion, it should show up in the Post Process dialog.
I'll post an update with install locations for other versions (Windows, Mac App Store) separately.
Jeff