How do i Size:Lerp() from a point?

So, this is pretty complicated but i really need help with this.

I'm trying to create something like this

The thing is that i got the Size:Lerp() thing right, But whenever i try to Size:Lerp() the part, it resizes the part from the MIDDLE. I am trying to resize the part from a surface, the BACK.

I just can't seem to get it working.

Does anyone know a solution to this? Thanks.