Another options is to go to the notation window and click on the # sign events editor and insert the patch change where you want them. Just tested it out and put a piano in the first two bars with Vibes starting at just before the last note of bar two. The last note of bar two now becomes a pickup to bar 3 and the last note in bar two and notes following are played by vibes instead of piano, then half way through bar 6 I changed it back to piano.

This seems to be what you were going for?

PM