Stretching can also be done if the Product is an Additional Product:

It's actually quite easy!
You just have to place a stretchable product under a Parent Product, and you're done!

Additional Products Stretch Measure Parameter

If you want Additional Products to stretch/move according to other Measures within the Product, like:

You can do so by assigning an Additional Product Stretch Measure Parameter. This connects measure parameters from an additional product to an assigned measure parameter from the Parent Product. The assignment allows them to stretch together in model space.

Each Measure can have one or multiple parameters from the Parent Product itself propagated to the assigned parameter. A checkmark next to a parameter in the “Propagate to Model Measure Parameter” indicates that it is being propagated.

Firstly, add a measure from the Parent Product under the Additional Product:

Then assign Measure Parameter(s) to the Measure in Edit Model Measure Parameter: