Shimano ultegra 11-28 to 12-32 options?
To use older 10-speed Shimano shifters such as Ultegra 6700 with cassettes larger than 28t, you need to use a 9-speed MTB derailleur.  You'll be able to handle cassettes up to the largest specified for the MTB derailleur (and likely a bit larger).

Shifting won't be as good as a full Ultegra 6700 drive train, but it will work.