In the Flowchart Palette, there is an End Loop shape that is a rectangle with both bottom corners cut. This can be used for the UML frame when you add a small white rectangle to mask the left side and then convert both to labels. The label is attached to the top left corner of the frame. This can be done for either a plain rectangle frame or for a group rectangle frame. See the attached UML Frame graphml file for examples of both.
There's not much you can do about the radius of the corners on the rounded rectangle.
I have created a frame title box that you can resize. It uses a unique combination of labels to mask the left side of the Flowchart End Loop shape to approximate the shape of the UML frame. It looks OK on my screen, so I hope it ports correctly.
This new shape can be placed in the top left corner of any rectangle to create a UML frame, and can be converted to a label once you have entered your text and adjusted the size.
The UML 2 Frame graphml file contains the shape.
So. It was more simple than I thinked.
I did it with converting to label a shape named Card in flow chart and then write property Rotation Angle at 180 degrees. See example in question description.