Hi kristommc
Unfortunately you can't in DIP
You can use teh ruler edges and if you zoom in you can get it pretty exact - teh rulers also move - sideways and up and down so you can move the rulers to your shape to ensure you are exact as possible.
Otherwise you can size each individually on its own canvas using Format Size
Open a blank Canvas and go to advanced to resize the canvas to the exact masurements you want.
Then fill that canavs with a shape and then drag that shape onto your layout. Fiddly I knwo but it works
Hope that helps