Robert,

This is how it works:

The triplet bar (one bar of ¾) should equal the tempo of half a bar of 4/4.
In other words divide the BPM figure of the tune (e.g. 140 by 2 = 70). This should be the total “length” of the ¾ bar. Since there are 3 quarter notes to be played in the same time span two quarter notes would take, you will have to speed up the ¾ bar tempo. If you want to retain the liberty of changing the tempo of the song in question, you should change the tempo of the ¾ bar not in absolute figures, but in percentages.

The ¾ bar should be increased by 1/3 (= 33 %).

While in the “Chord sheet window” right click on the bar in question, select “Bar Settings” (F5), change “# beats this bar” to 3, in “Tempo change to” or “% change in tempo” enter the result of the above calculation. Also select an appropriate waltz style.
NB: For the remainder of this bar, which will become the next bar if the triplet is in the first half of the original 4/4 bar (or the other way around if the triplet occurs in the second half of the original 4/4 bar) change the “# beats this bar” to two and change both the style and tempo back to the original style and tempo. In the bar after this change the “# beats this bar” to four.

If I am correct this will only work with MIDI styles, so e.g. no real drums.

I have use this method in a.o. my arrangement of “ It’s a Blue World”, where it sounds great to have a triplet in the first half of bar 6.

Good luck!
Tonnie