Sorry for the provocative title, I just could not help myself!
This study http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0169486 seems quite convincing but has little to do with the Clovis question. Still, is seems incomprehensible that humans would just sit there in those caves for 10 000 years, waiting for the ice to melt down so they can venture further down south. There would have been nothing to prevent them to explore the coastal route much, much earlier. Of course, that could hardly ever be proven, with all potential sites under water.
I hope more knowledgeable folks would come forward with the latest info.