Do supersets, multisets where you do 2-4 sets with little or no pause at all, working different parts of the same muscle group in each subset.
(For instance reverse curls, curls, hammer curls, curls where you lean forward.)
Some exercises require so much energy that you can not do your normal amount of sets in such a "short" time, but then again, you've most likely already spended your normal amount of energy, thus the net result will be the same.