I don't. The source code for the handwriting recognition is not available, so the onus would be on Nokia to do it. And they have chosen not to do so. Can't blame them, it wasn't really great in the first place and I do remember a fair few complaints...

The handwriting recognition is not fullscreen; it does run in a little window on the bottom of the screen. Which poses a problem as the Fremantle UI is not really tailored for stylus usage as such (the widgets are a lot bigger and a lot easier to hit with the fingers [they're also a lot nicer, too]). So if you copy the relevant files from a Maemo 4 device, it may work on the N900 but Stskeeps has a picture (somewhere) of the stylus keyboard copied from the N800 running on Mer and the result didn't look...um... shall we say... appealing.

Personally, I think helping the guy doing https://garage.maemo.org/projects/cellwriterhim/ is a better bet.