To the OP. I looked back at your original thread and I suggest another alternative, a trailer. I like this one. It handles well and won't slow you down much on the commute when not loaded but actually handles quite well under load (better than loaded panniers). There should be no problem using it with your current bike.

For my IGH bike I use a Rohloff with dropped bars. I like this mounting solution for the shifter very much but, alas, it will only work with a wishbone stem.