You can - it's just a bit ... tricky.
Since it won't send multiple continuous key combos you have to try to press the keys in close enough succession that the receive buffer counts it as a single keyscan
Usually takes me 4 or 5 tries - rather frustrating, and about the only downside of this nice little device.
Edit : hrmmmm. OK - scratch that - just retried it on my XBMC machine, and I can't get Ctrl-Alt-F(x) to work
at all any more. I *swear* it used to :o but I haven't tried it in a while, and it seems that somewhere along the line after fiddling with lots of kernel updates, & LIRC configs etc it's died.
Looking at
xbmc.log the Rii's Fn+Enter [Ctrl-Alt-Del] gets sent as three simultaneous keyscans, so I'll play around with keymap.xml and see if I can get that transmogrified into Ctrl-Alt-F1 somehow.