I went the same way, admittedly i never crashed it or broke it, the best way is tell him to pay for the upkeep, Tax, MOT, Insurance,fuel costs and servicing.
I saved on the servicing doing it myself but try these for figures
at 19 years old in RM11 area:
1995 ZX6R F1 Third Party Fire & Theft insurance - £1500 per year
Road Tax - £48 per year
MOT - about £25-30 a year
Fuel - 18 litre fuel tank so look about £22 per tank and running correctly you should see about 160miles to a tank.
can he afford to do it?
I did it when i was 19, and if i knew what i knew now....i wouldnt do it, it would save me a lot of aggro....admittedly it would have saved me some SP30's aswell.
If that doesnt work, he has 6 points for 2 years on his license, 2 SP30's and its revoked under new drivers act (like me) and i learnt my lesson pretty quick. got a VFR400 NC30 now lol.