uefi - Set nomodeset in usb installation (efi loader with iso)

I'm working with the studyblast solution to creating a live USB on OS X. I managed to get Ubuntu booted but the screen looks like a corrupt/glitch image. I can just about make out the clock on the bottom right and a few icons. I've been told that this is easily fixed and that nomodeset needs to be set for the graphics card. But all the solutions I find are for Ubuntu systems installed to hard drives. Where you can cd in and edit the grub file - how do you do this is if it's in an iso?