How do I Slide, Pivot, Catapult from a movable platform?

Greetings,

I've watched a dozen or more training videos, and read through countless pages of tutorials and educational material, but I'm not sure that what I'm trying to achieve can be done the way I'm going about it. Maybe someone can point me to info that I might have missed?

Here's what I'm up to:

I have a shooting apparatus made up of 4 separate sprites - a Base, a Pivot, a Slide, and a Projectile... and of course there's a ground plain w/walls, etc. The Physics Catapult template was good to test drive, but I've hit a wall. ;-) Here is a visual representation of the layout:

And here is the CAPX file: http://www.webmagi.com/media/uploads/scirra/Slide-Pivot-Catapult.capx

I would like the whole apparatus to be movable, vertically, (without activating or firing the projectile on release) and I would like the slide to control the pivot after the height of the apparatus is set. The pivot should move up or down on either end, but remain attached in the middle, pivoting on the base. The slide should also control the projectile, or at least they should move in concert until released, and then it should return to its original position while the projectile is fired. So basically I'm trying to build a shooting mechanism from 4 separate graphics, and trying to find at way to bind them programmatically. Can this be done?

I first attempted to use Spriter to generate separate animations, but the freedom of movement I need for aiming (high, low, forwards, backwards) in tandem, while holding the projectile with a finger doesn't seem possible. Is it?

Anyway, surely this is not a one-off idea. There must be examples, or information that would help fill the gaps in my knowledge. Any help would be greatly appreciated.

Thanks.

Here is a better description of what I’m trying to achieve: https://youtu.be/jaLWHBlhSmQ

I forgot to mention that in the video, the capx file I'm using for the demonstration has R0J0hound's Chipmunk2D addon.

Here is an updated capx with that addon: http://www.webmagi.com/media/uploads/scirra/Slide-Pivot-Catapult-2.capx

If my idea of creating a lever attached to a pivot, which slides along the top (and acts like a tension spring when pulled backwards), while also being able to pull up or push down on the pivot at every point along its entire length can be achieved with the default Construct 2 physics, then I would be very interested in learning about any examples or documentation referencing such mechanics that may exist.