The event_google trick explained a bit more:

Open up an adb shell, and enter:

echo '1' > /sys/android_touch/event_google

And it could enable the pen. To get this working permanently without having to do this manually, the developer has to integrate it into the ramdisk. But it's probably better to try it this way manually first.
Devices I have: HTC Desire, HTC Flyer

Member of XK Team, delivering CM and MIUI goodness to the HTC Flyer

Donations by Paypal: corepwn20@gmail.com