Syncing between two itunes
I purchased a song on my work computer which is one of my authorized computers. I however, sync my music with my home computer which is my main library. I want to transfer just this one song on my work computer to my iphone. However, whenever I try to sync I get the message "All existing songs and playlists on the iPhone will be replaced by the one on this library". I just want to sync one song and I am logged into both accounts with the same username. However, my home computer doesn't see this song and it is only present on my work computer. Why is such a simple thing made so complicated and maybe impossible by Apple?