You could just go low-tech and repeat it in an inline comment either above the it, or after the semi-colon.

If the stuff you want to fold can be matched with regex, you may be interested in Is it possible to collapse custom regions in the middle of lines?, but I don't know if it will work given that you already have a folding provider.

As a curiosity (yes, I read the part of the question about the impracticality of writing an extension when another extension already contributes a folding provider), you might be interested in How to write VS Code extension that folds specific regions and renders an inline summary of the folded region?.