iPhone Sync to iTunes - Erase All Data Problem

I rarely use iTunes for any syncing except custom tones and stuff. However, when I got a new rMBP and replaced my cMBP, I did not transfer over my iTunes folder. Reason being, there were a ton of movies I had on there that I rarely watch and would take up space (waste) on my 500gb SSD. I deleted my old TM backups and folder backups of my old computer because I thought I didn't need them.

So the minor problem now is if I try to sync my iPhone to my new computer in iTunes, it's not it's home so it wants to erase the content on the phone and sync.

What's the best way to deal with this? It's not a huge deal but it would be nice to sync sometimes. Especially creating playlists and stuff.

Thanks!