No way to do it since there are 2 kinds of PR: ToolBar PR and the PR computed on the fly by Google's algo. Toolbar PR is the green line you see on your toolbar. It's always outdated and does not really reflect much anymore. Besides, it's almost sure that teh PR algo is much more comlicated that the formula in the original research paper by Larry and Sergey.
I dont trust on page rank prediction tool. I have been checking for good few months and it never gave any accurate result compare to google update.
well, Google can predict PR. If you get PR5 backlinks then you could expect to get PR3 or PR4 but there's no accurate tool to predict PR.