Sync iphone over wifi

My Iphone 4s is slightly broken and it means it does not recognise if it has been connected to a power source or a computer. It does charge, however, when i turn my phone off so it is usable. Unfortunately I recently tried to upload some more music onto it and i realised I couldn't as the computer did not recognise it, and I hadn't previously set up wifi syncing, so now i don't know how i can get the music on to my phone. Thanks.