[CentOS-virt] Sending function key like F12 to a booting cd

Under Xen I am booting a virtual server from a recovery CD-Rom (actually a iso image)

When the cd boots in the console window I have to send the single key "F12" to the window within 10 seconds from start, otherwise it will try to boot from harddisk.

Pressing F12 in the console window does not work - and I tried sdl as well as vnc.

I can send various Ctrl+Alt-combinations using the menu item "Send key" but not Fn keys.

Does anyone know how to send F12 or other function keys to a booting cd ?

...torkil... on centos 5.3, xen-3.0.3 and virt-manager 0.5.3.