Found this on another website but haven't got around to trying it out yet, maybe someone else here has tried it already and can let us know if works.
Using ipod Agent
1. First install either ipod Agent on PC, this will run a small server program to listen for the Android device.
2. Connect mobile to pc via usb and create a folder called Music on sd card or phone storage, using usb storage method in wireless connections, not using Kies default.
3. Right-click on iTunes Agent icon in system tray and choose preferemces.
4. Leave the settings at defaults and click new.
5. Enter the device name, Galaxy S2
6. Leave Synchronize pattern: set to iTunes
7. Click the Choose button and select the Music folder you created on the Galaxy S
8. Click the Create button and select the Music folder you created on the Galaxy S
9. Click Save and then Close
10. Launch iTunes and you will see a playlist folder called My Devices, under which you will see the Galaxy S
11. Simply drag the music you wish to synchronize from your iTunes library to your Galaxy S into this playlist
12. Finally, right-click on the iTunes Agent icon in the system tray and select Synchronize devices to sync Music to your phone.
To enable usb storage mode access only when connecting to the PC - go to Settings, Wireless and Network - USB Utilities, you have to press button again once connected to allow access.