my own portable app - emacs

so, i tried just copying over my emacs directory and putting the binary into pstart, and it seems like the only thing that is keeping me from having a "real" portable app is that i don't know how to tell emacs to look for me .emacs config file on my thumbdrive rather than in the emacs directory that it usually is in on my windows machine.

I'm sure this problem has been overcome with other portable apps . .

is there an easy solution to this?

if so, what is it?