Another thing you can try, along the lines of what Kings is thinking, is that you can right click on almost any parameter in FL Studio and click 'Create Automation'.  This will throw a slideable automation event into the playlist that you can use to automate the parameter.  for example, right click on the pan button for one of your sounds and click 'Create Automation', then go to the playlist.  There will be a colored line at the bottom that you can stretch out and slide up and down, effectively automating the pitch for as long as you care to.  (and thats an ancient chinese secret, right there!) and thanks, Kings.