Can the size of a shape layer be defined by the size of a text layer (using an expression)?

Hi everyone,

I'm working on projects that involves many text boxes - text on top, and a rounded-rectangle shape layer behind. The distance between the edge of the shape layer and the edge of the text layer needs to be consistent (for the moment, let's say 20 pixels separation all the way around). Is it possible for the size of the shape layer to be defined by the size of the text layer, so that I don't have to (tediously) measure out the size of the shape layer every time I have a new text element? Is this something that I can do with an expression?

Thanks!