Zoom/change screen resolution in Startup mode

I'm posting for a friend who has vision issues. He's attempting to do the clean installation on his 2012 MBP non-retina with Mavericks. Basically he's having some trouble reading small font size in the Startup environment with the bootable Mavericks (and likely next steps once the installation is completed). The problem is the shortcut command for Zoom in appears to be disabled (which I assume Accessibility or shortcut commands is/are disabled in this environment) and seems there is no way to change the screen resolution in order to enlarge the size of the screen and font size. Any suggestion to remedy this situation?