Smart shape enclosures

[motet]

I guess there's no way to have enclosures for smart shapes? I want to have

smorzando - - - -

cross barlines between staves. It would be nice to give smorzando an opaque background. (I can break it onto an expression and a smart shape, of course).

[Peter Thomsen]

If I understand you correctly, you are talking about having an enclosure around the text part at the beginning of the smart shape, not around the entire smart shape, right?
I mean, only around the text smorzando, not around the dashed line after the smorzando, right?

I would -

1) enter the smorzando as an expression.
You can give an expression an enclosure, and make it opaque.

2) enter the dashed line as a smart shape.

To make sure that the horizontal distance between expression and smart shape is always as desired, I would make the expression justified right, so that the end of the text is attached to a beat.
Then, begin the smart shape on that beat.