If it's an IR PS3 remote, you do it the same as most every other IR remote.
Now, if it's the Sony Offical PS3 remote, then it's actually a bluetooth remote, which means you're out of luck [as explained if you try to just manually add the device in your harmony software].
There is no hope for a firmware upgrade to resolve this situation either, as the remotes just aren't designed to do Bluetooth.
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If it is an IR remote, well, ya gotta tell us which IR remote and usb plug ya using at least
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and I look like an idiot, really didn't see the link.