Before proceeding, this is very much in the development stages and is a work in progress. And no one shall be held responsible for any damage might caused to your device. Do it at your own risk.
Step 1: Download these files from Hotfile:
Step 2: If you have Samsung KIES opened, shut it down completely.
Step 3: Open ODIN.
Step 4: Shut down your Galaxy S II. After it's shot down, and then hold these altogether: Volume Up + Home + Power while booting up to enter Download Mode.
Step 5: Plug Galaxy S II to your computer using USB. ODIN will then detect it.
Step 6: Click PDA and then choose: I9100_CODE_I9100XXKP8_CL42141_REV02_user_low_ship. tar.md5 that you put on your desktop earlier.
Step 7: Now Click PHONE, then choose: MODEM_I9100XXKP8_REV_02_CL1092599.tar.md5
Step 8: Now it is time to click CSC, choose: GT-I9100-MULTI-CSC-OXAKP8.tar.md5
Step 9: Now click START.
Step 10: Now ODIN will be doing its job to flash the leaked ROM to your device which is the Galaxy S II. When it reboots, then reconnect it from your computer.
Congratulation now a leaked early build of Android 4.0.3 ICS with TouchWiz is already installed to your Galaxy S II now.