In my experience, Finale often doesn't playback what the notation suggests. That's why I (and several other composers I know) often have to create two different files - one that is correctly notated (but doesn't sound the way it should) and one that Finale plays correctly (but isn't notated the way it should be).
That being said, sometimes you can work around Finale's limitations by hiding extra commands. This method can get over-complicated, though. Perhaps you could set tempo markings for the minimum and maximum speeds of the notes in the left hand, then add an accel. and rit. to smooth out the tempo changes. Then right-click the words and deselect the 'show' command, so that the words will be hidden when you print the score. However, you'll probably have to do some math and input a different, hidden time signature than what is notated (and extra, hidden rests) if you want the overall tempo to stay the same (a tricky process). Alternatively, you could try to hide the barlines and draw them into the score yourself in the right place(s).
There's a thread here that you may find to be useful. Maybe there's an easier way to accomplish what you're looking for, but in the meantime, I hope this helps!