Call 1: "Eighty"
Call 2: "Ninety"
If no response - STOP! (or "abandon" as my not-for-much-longer current lot prefers).
That should mean that the stop is initiated at no more than 100 kt. - and I sure hope that none of our FO's get through the training system without being able to acomplish this safely.
Look at it this way - if they cannot manage a stop from 100 kt. - what do you think their chances are on a single-pilot circuit? Or a diversion, for the matter? Or surviving another bad decision they make while on their own?
Even if we do a 40-kt overrun, we'll in all likelihood all walk away from it (with the captain being the only possible exception to that rule).
If everybody is so worried about FOs handling a 100-kt.-abort, we shouldn't confuse these poor, feeble individuals
any further and simply stay the party line: "Follow your operators SOPs".
Sometimes I really wonder...