CentOS virt - Oct 2009 - 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.