Feature request: Custom selection crop tool

Hello,
 
is there a way to add "Custom selection crop" feature or some kind of crop preview that could be applied on RAW file during culling? This would become very handy when checking composition of the photo. Right now, I have to switch to 3rd party program every time I need to check composition using crop feature.
 
For example, IrfanViewer has this very handy crop selection feature:
- applied custom selection can be adjusted or moved by using right mouse button and holding CTRL etc.