what I suggest is workaround only
get photofiltre 6.5.3 - it is old, no longer developed, but free photo editor and it has some awesome functions. To test it, download the portable zipped version
- use plugin that other app to open photofiltre with it
- make rectangle selection (any size) , right click on the selected area, a menu appears - go to manual setting and enter dimensions, okay it
- right click again and click on first option in the menu and chose color of border and okay it. The selection changes to rectangle
(sorry if my description of photofiltre options is not precise I only have czech version)
Off topic: Photofiltre also has polygonal selection and you can store and reuse selections.
And I just love the Photomasque function for making frames