Does anyone know a custom plug-in that uses a CDT as an input?

There should be many like that in shared components. one of them is execute stored procedure by james.carter , this one has Input as CDT , search CDT in shared components.

Thanks Rayudu - do you know one that takes CDTs of type multiple as an input?

Looks like the "Export CDT to Excel" has an input of CDT of type multiple.

Do you mean this one: "Export SQL and Report Data to EXCEL - V2". I can't find Export CDT to Excel. Do you have a link?

Correct, it's within that plug-in.