ITunes help needed......?

Ok I have a single ringtone I created from an app on my iphone. Ok, I am currently not on the computer I normally sync with so its an empty library. I was able to get the ringtone off my iphone with filesharing without syncing but I cant get it on my iphone with out syncing and if I sync it says it will replace all my current songs with the current library which is nothing. How do I just sync this single 30 sec audio file and keep my current music library?