It didn't help with the raccoons, but it did help with the possums - we put up a "table" we built - the legs were inset and the top was boards with a few inches of space inbetween them. Then you can place a feeder up on the "table."
Of course, in the end, we ended up just having to put food out in the morning and in the evening and taking it away. We left it out for about an hour and a half before taking it up. They quickly learned when the food was available, and it discouraged the night-time feeders.
If you haven't already trapped these cats to have them spayed/neutered, you really ought to - both for their own health and well-being, as well as to help prevent more homeless cats. You can use the link in my signature line to help you find low-cost services.
You can also use this link http://www.pets911.com/organizations/organizations.php
to help find organizations in your area that can help, or that may be able to lend a trap - or may know of low-cost spay/neuter services in your area.