I think you can package in x64 using this
It has more options that are hidden in modern udk builds.But you have to make a list of maps(like in old ut3) and its something i just cant remember on how it was done.In the cook options i do see stuff like cook for x64,ps3, and even some xeon stuff???(what?) and i think dx11(but cant remember on that)
If someone figures on how to make it work,please let me know.