I wrote a script that does this...but unfortunately it's for Unity. So if by some crazy coincidence you're working in Unity, I could share it with you.
Oh I found something kinda like what I want but its just for 3dsmax :/ A stand alone application would be ideal for me, like xnormal but just for packing objects into one sheet. http://www.scriptspot.com/3ds-max/scripts/texture-atlas-generator