When defining partial drawing view, besides the view boundary reference point you also need to sketch spline-shaped view boundary.
Product idea is to have, additionally to the spline boundary, also predefined boundary shapes available, e.g. circle, square, rectangle (with possibility to create your own or even to load them from the sketch library already available in Creo) not to sketch spline everytime, where you might need only rectangle. Shapes should be modifyable in a way to be able to either drag corners to deform rectangular shape and to drag sides or arcs and not to loose rectangularity (similar to *CAD Box object).
Spline shaped drawing view boundary (currently the only option)