I checked with a few of our scientists and they all stated pretty much the same thing. Connect the columns with either a 1uL (430001516) or 2uL (430001264) loop as the connecting tube(s). Work involving connecting UPLC columns in series at Waters used the Column Manager which enables you to easily use multiple columns. However, if you have the Column Oven, it is much more difficult (challenging) since the Column Oven was designed to accomodate one column only.
I hope this helps.
Did you have much success?