Di2 Ultegra "Shifters"

smitton Posts: 13
edited July 2012 in Road general
I want to build a TT bike using Di2 Ultegra. Question is, if you use aero bars what do you use for electronic shifters? Has anyone seen (or made their own) button shifters that could replace the brake lever shifters. What are the pro's using? Why can't a simple push button switch be used?
Thanks for any help.