I'm not sure why only a subset of options is available. I would blame the outdated webkit version, but it doesn't really explain, fully.
Hiding the cursor via transparent image (1x1 transparent .png), as you mentioned, seemed to work just fine using the following:
* {
cursor: url(image.png), auto;
}
You would probably want to target something more specifically (maybe?). I used the star selector just for demo purpose :)