Installing Windows 7 from USB using rEFIt

My Superdrive is busted, no surprise there. I have created a windows7 .iso and formatted my USB using diskpart and copied over the contents of the cd. rEFIt is able to see the USB but when i chose to launch the installer it displays:

'Boot disk not found - please insert boot disk then press any key'

Can't move on from here. The other options i have which are to boot a couple of .ini files just return an error.

Not sure where to go from here.