Key stroking fn + f8

I need to make an applescript to press the keys fn + f8 at the same time. The only problem is those are both keys without names!

tell application "System Events"
    key code 63 -- Will press the fn key
    key code 100 -- Will press the f8 key
end tell

However, how can I get these two key strokes to happen simultaneously? I cant seem to do key code 63 with 100 down or any variation. Help?