Not if you want it applyable by Lightroom, but if a plugin is the only thing that can apply it, then it could be made uncopyable using ordinary software keying techniques.
i.e. user must have a key and the software (plugin) to apply the preset (if the key is valid).
Once the preset is applied to an image (even by plugin), you can still create a new preset out of it.
Why are you so afraid of copying? The world is full of free presets already
Good point - you'd only be keeping already honest people honest that way...
oh, well mainly that several people have inquired about creating plugins / presets that they would sell (hence the copy protection), and integrate into the LR ui. I figure I'd ask as in the long run it would be nice for bigger players (eg. alienskin's / red giant's / nik's of the world, etc.) to integrate their stuff directly into the UI versus having a separate UI, and I'm pretty sure they wouldn't want their stuff copy-able