For what it's worth, the "and" is mandatory in my language and we manage to disambiguate 100 2/3 from 102/3 by putting a pause between either "hundred" and "and" or "two" and "thirds".

100 2/3 - one hundred ... and two thirds

102/3 - one hundred and two ... thirds

Alternatively, use "plus" instead of "and" in the first case.