beamed quaver notation with 3 over.

In some music notation you can find a beamed triple quaver with a "3" over it, meaning three equally long notes are played in succession and filling the space to the end of the bar (which often is not exactly 3 quavers long but plus or minus a bit) i have come across it in notation from 'Les Mis' and other manuscripts.
The manuscript I'm trying to transcribe for inclusion of English lyrics has just such a case: the actual length available is one quarter, but the notation uses 3 quavers with a 3 written above the beam. If one writes in three quavers, Musescore put the last quaver in the wrong bar, putting all the rest of the mss. out. I have tried using two dotted semiquavers plus a quaver, and written a staff text "3" above it, which fits the space, but it doesn't exactly look elegant. Is there a better way, or a method for entering this kind of notation hidden somewhere in musescore?