Hi Jon,
I'm not sure what you are trying to do. If you wish to make it
understandable that a text is scrollable than you can use Text Area widget
and turn on the scrollbar in Properties View, or you can use a regular Text
widget with Vertical Scrollbar widget alongside.
However if what you are asking for is actual interactive scrollbar then
this is not possible. WireframeSketcher is meant to be used for static
wireframes with only simple interactions added via links.