Is it possible to create a FCP effect inside Motion that puts an opaque box behind a title?

As a novice Motion user, I’m curious if it’s possible to create a Final Cut Pro effect inside Motion that applies a text box to titles inside FCP. My goal is to be able to apply this effect to any title inside FCP and a text box can appear behind the title’s text and will automatically resize depending on how much text is present in the title.

So far, I’ve began attempting to create such an effect by having a Motion ‘effect source’ layer with a ‘box shape’ layer linked to it with the ‘align’ and ‘link’ properties. So far, the box will show up behind the text but it won’t automatically resize depending on text input.

Any suggestions on getting this to work?

Thanks in advance!