Controlling PlayRate of Lift Sequence with Vertical Controller Position?

Hi gifted community
Problem: I am working on a museum installation with a virtual vertical exhibition tower.
The visitor travels up and down this tower with a lift. This movement is controlled by a level sequence lifting the vertical position of the VR-pawn continuously and very slowly…

Aim: The player should control his/her vertical movement using the vertical position of the controller - if the controller is held low, the lift should travel down, and if the controller is held high, the lift should travel upwards.

Question: What is the easiest way of getting the delta of the height between the player and her controller and to feed this value into the playrate of the sequence player?

Many thanks for your brains!
Mischa