The amazing thing about lead tape is that even small amounts are noticeable on swinging.
Also, it is incredibly easy at the courts to add and take away bits of lead tape to get the feel you want.
So rather than forcing your son to take such a big jump, why not just add a little of lead tape at a time to the racquet?
Bring lead tape and scissors to the court.
CUSTOMIZING RACQUET WEIGHT & BALANCE http://www.tennis-warehouse.com/lc/customize.html
The Official Lead Tape Placement+Racket Customization Thread