First you need to make the USB flash stick bootable by writing the Windows 7 ISO to it using Universal USB Installer
with Windows 7 in dropdown menu.
Then access the one-time BIOS Boot menu key at boot given in Theog's post to see if it registers, possibly under HD's.
If not borrow a USB DVD drive, or take out the HD to place alone in another computer to install, then SysPrep to move HD to another computer
before moving back to target machine.