I really don't have this happen very often since I do a lot of climbing rides and drafting is of very minimal help at 5 - 7 mph. When it has happened it's never been a big deal.
Sometimes I'll let the drafter sit in for a few minutes, then motion them to come around. Most often they do, we trade pulls and it's all good.
If I were to get a non-cooperative drafter I would either speed up and see if they could hold my wheel (most likely they could) or just slow down (as noted in the posts above) to the point where drafting just didn't make sense (depending on my motivation or lack thereof at the time).
Rick / OCRR