Kudos to Joerg and his video for inspiring me to think of this.
Joerg pulls his the trigger mechanism 3 meters before locking it in place.
This is my idea.
I have a 48" length of telescoping steel tubes that were made for holding heavy drapes.
You could use wood or metal to achieve the same effect.
A conventional Y slingshot is mounted at the front end of the outer tube.
A second handle is located somewhere along the outer tube.
A third handle is located somewhere along the inner tube (that pulls out) that has a trigger mounted on it (not the mechanism).
The tubes are at the minimum position.
You use the portable trigger mechanism and grab the pouch and the projectile.
Place a foot on the SS handle for the first draw position and pull the mechanism and fit it to the inner tube.
Grabbing the 2 handles you pull out the inner tube until it reaches its draw length where it locks.
A string or a wire connects the trigger to the mechanism.
Not a 3 meter Novitzkenegger, but a much longer than 160 cm butterfly weapon; perhaps 2 meters.
Do you understand this design?