Now I get ya.
Glad you found the visible field in the system properties portion of the web part.
For widgets, one limitation is they don't allow macros outside of the default value set when configuring the widget itself in the widget utility. So you can't add macros by default when adding the widget to the page.
May be possible to add a new field, allow them to enter macros then in the web part code render the macro and disable the display of the widget manually.
Also not sure if you can put a macro in the default value that references a widget property (so the use can set a property which the macro in the default value will I'll in and use), may be worth a shot.
Sadly the one downside to widgets.