well, if you freeze a thin layer of ice into the ice cube form, add the mentos and rest of the water, then freeze again you could time the mentola-bomb by means of how thick the first icy layer is...
Anyways: it won't "explode", it'll just foam up like stupid...
It wouldn't work, because the Ice doesn't melt all at one time. It may foam up alot, but no explosive foaming. Also, DC and Mentos isn't as noticeable in an open-top glass because there is not pressure from the foaming reaction.