Sketch Prototyping: Sticky Footer beneath the fold

Hi community

I need a way to achieve this:

sticky footer in Sketch prototype, but the footer must appear after a certain value of scrolling down.
For example, scrolling down the Prototype and when reaching beneath the fold, the sticky footer will appear.

A very common way sticky footers nowadays work, but I don’t find any way to achieve this in Sketch.

thanks for your feedback