Child to object with blend shapes

Hello i have a mobile cran 3d model that has blend shape for the telescopic boom extension. Is there any way i can add my hook ( with rope physics) under the end of the boom and it will follow when i change the shape key from 1-100?.

The 3d model had the boom extension with drivers etc in blender but the driver did not work when importing it to unity so in some strange way i managed to make the boom to shape key.

Im new to both blender and unity and could not find anything that explaned if you can get a child object to follow the shape key.

 

Make a sincronical animation for rope root, then control blendshapes and root animations simultaneously.
Also take a look ot my plugin for vertex animations. It allows to add points that follow animated surface. In ship demo the ropes is constrained to sail`s corners and follow on its animations.

 

I have a similar issue but with eyebrows and a character customization system which uses blend shapes for the facial structure.

Anyone have some clever solutions to this, also @polyflow3d, your link appears to be broken, would love to check it out.