Get an official response but I am 95% sure it would depend how the plugin works.
As I understand it you cannot restrict a file or force a buyer to be tracked in anyway (not sure how a plugin like this would work unless it tracked where it as being used?) .
Check this out for possible reasons why: Protecting your Theme by Activation Codes/License Keys
It strikes me that if this was as simple as adding verification then just like many other seemingly obvious features etc. envato would have already instigated it.
Unfortunately this may just be part of selling stuff online (it’s not an exclusive problem for authors here).
I think you do need to be careful and make sure you are in the right before initiating anything like this and the way some authors have ‘voluntary’ code entry for things like auto updates may be the closest you will get.
I am more than happy to be proved wrong and completely on your side about stopping the piracy etc. but fear there is a bigger picture to consider.
My advice would be to contact support for an official answer.