You will not be checking car tweak with this method. By lifting the front you will be checking rear tweak _and_ front droop, by lifting the rear you will be checking front tweak _and_ rear droop. When for example both front droop and rear tweak are off the same amount, you can miss it. So this method requires your droop settings to be perfect as well, then it works OK.
The only way to check tweak at ride height is a tweak board or corner scales.