I have checked the FAQ and it seem that in my case it cannot be done.
Support writes:

• Quarter note triplets will never display properly if they span beats 2 and 3 in any measure.

The song I have problems with (The melody line of a blues called Going to a Meeting by Pat Martino) has a quarter note triplet on beats 2 & 3 in the second bar (and again in the sixth bar).

So again I have to ask if somebody has found solution.