1.Enable administrator account and set a password for it.You can refer How to enable or disable administrator account in windows 7
2.Logoff and login with administrator account
3.Relocate your user data to other non-system partion,for example from C:\users\J to D:\users\J
3.5 Delete old profile (or Original profile)
rmdir /S /Q C:\Users\J
Note:Do not forget to delete the old profile folder if it’s been relocated successfully
4.Use mklink to create a symbolic link from C:\users\J to D:\users\J
5.Re-login use your own ,you will find nothing changed,but in fact your physical user data is on drive D.
6.Done.The next time you re-install your OS ,just use the same user name, remove C:\users\J then run the command of step 3 again then your user data is back.