Type straight quotes (",') when smart quotes is turned on
I added " and ' as replacements for something, then the replaced quotes were not converted to smart quotes in a few quick experiments. For example, setting "" and '' to be replaced by " and ' respectively:
Typing ""foo"" ''bar'' resulted in "foo" 'bar' with normal quotes. As shortcuts go, just double tapping the button instead of single tapping makes for a convenient shortcut.