The idea conversations I copied links to came the closest to enabling what you want of the currently open conversations that I found.  (You can achieve the effect of a one time penalty if the frequency the penalty is applied is only possible once during the time late submissions are available for the assignment.)  I recall that there was once an idea about flat late penalties, but it is not coming up in my searches.  It must not have achieved enough support in the old community.  You would have to start that conversation again, if the existing conversations do not meet your needs.