I believe dmertz is correct as he knows quite a bit about this. But more simply stated, yes, the end result of your proposed action would get you what you want...the trouble is, The IRS doesn't allow you to do it that way (if they did, I would have gone that route a long time ago). I looked into how to do this (separate pre from post tax contributions so I could roll the after tax into a Roth) for a long time before I stumbled upon the 401K solution. Without a 401K, I don't know of any other way to accomplish this.
