NOTE: This involves editing a game file so create a backup copy of the file beforehand.
Use a text editor to open the defuser.ini file in the drive letter:\ea games\harry potter and the chamber of secrets\system directory. Locate the following text:
[HGame.Harry]
bInvertBroomPitch=False
bAutoCenterCamera=True
bMoveWhileCasting=True
bAutoQuaff=True
fDamageMultiplier_Easy=1.2
fDamageMultiplier_Medium=2.0
fDamageMultiplier_Hard=3.0
Change the fDamageMultiplier values to something between 0.0 and 1.0 to take far less damage than you can ever imagine!