A bit more information is needed. In the 4/4 bar, are the quarter notes the same length as in the 3/4 bars? In other words, is the quarter note constant (thus yielding 13 total pulses) or is each bar to be the same length (the quarters in the last bar are only 3/4 the duration as in the other bars.) Both of these are legitimate possibilities.
If the quarter note pulse is constant, then three 3/4 bars followed by one 4/4 bar with each quarter note marked as a triplet would be easy to read. If the duration of each bar is constant, the last bar could be left in 3/4 and nested tuplets used. Either a big 4 bracket over the bar (showing the quarters to be 4 in the duration of 3) and eighth-note triplets underneath, or just twelve sixteenth notes but barred in groups of three instead of groups of four (slurs over the groupings would help too.)