Datum are datum.
Many UK airfields have up to 60ft difference between threshold and the ARP so setting zero on the apron will not help much.
It also won't give you the correct separation from other traffic. If you are flying QFE or QNH it is not up to you to adjust as you see fit.
If you are flying from a strip or field that would be different but the datum are there for reasons greater than our own visual acuity. Do you really spend your last 50ft looking at the altimeter or looking out visually!