Code:
# echo mem > /sys/power/state
(requires root I imagine)
"should" do it, but I'm not sure that's exactly what the hibernate does - everything seems to sleep but the reader side doesn't change to display the wakeup instructions and I don't think the power led went from solid to blinking (not surprising - there's probably some hibernate script I'm missing that is triggered when you close the device)
finding the actual hibernate script would be best, I'd think...