Yep, tspressure does work.
I have it working with the 1.3 beta (look at the Japanese page for the download) but what isn't stated, and you need to translate the Japanese page to find this out, is that you probably need to calibrate the application against the values that the touch screen is sending out.
If you open up the menu and select Other->Pen Pressure... then you can input values for min. mid. and max. The page suggests values of 100, 200 and 220, however, I ended up with values radically different on my SL-C860 so it may be model specific or specific to the values being pumped out by the version of the touch screen driver.
Version 1.3 does, however, provide a means to calibrate the pen pressure. If you bring up this dialog and stroke the stylus in the white area at the top of the dialog it will pump in some sensible values into the min, mid and max entries. I don't know if this option is available in the stable 1.02 software because I had moved on at that stage to the later version to try to get it to work.
Hope this helps...