If anybody wants to do this to their own GMail account without putting trust in a third party, this is pretty easy to do with the little-known Google Apps Script. You can write JavaScript that will run on Google's servers and do whatever you want to your account. (I use this to archive various automated emails if I haven't bothered to look at them, to keep them from cluttering my inbox after they're obsolete.) Here's…
This is awesome. I've been wanting to setup this functionality for a while, but wasn't aware of Apps Script. One thing missing in the above is to remove the 'hidden' label.
var buffer = GmailApp.getUserLabelByName('buffered');
function release() {
buffer.getThreads().map(unbuffer);
}
function unbuffer(thread) {
thread.moveToInbox();
thread.removeLabel(buffer);
}