Install Windows 7 on USB drive via Bootcamp (yeah, an other one...)

Hi all,

before all, sorry for my bad english... i'm french.

So, i'm trying to install Windows 7 on my iMac (with Lion on it) which is on an USB drive (done with an other computer with Windows 7 USB tool). Ok, no prob' for that but now... ?
I searched during many hours but i'm still stuck with Bootcamp. I've my USB drive with W7, Bootcamp and... nothing else and i don't know what to do with rEFIt

May anyone could help me please ?

Regards,

You need to clarify something for us first:

Are you trying to install Windows 7 on a USB drive attached to your iMac? Or, are you trying to install Windows 7 on your iMac from a USB drive?

2nd choice, i'm trying to install Windows 7 on my iMac from a USB drive

Take a look at these instructions. They're for a MacBook Air but the install method from the USB drive is the same. Let's see if it works for you. LINK

I even read that but now, we can't choose "install later" in bootcamp...

Take a look on attached files.

THE problem is, we can't create a Bootcamp part without DVD, and i'm searching a way to bypass that.

Anyone please ?