Sometimes browsing imageboard pays of and between the tons of trolling soem small software gem turns up.
In this case someone on lulz.net brought up a topic for a 3D sculting freeware still in devellopment.

At first i couldn't get much out of it but the alpha 3 brought pressurecontroll for tablets wich makes the limited tools way more usefull.

give it a shot but don't expect it to be all to stable...crahses quite oftehn when using the Undo function. (also CPU usage went up considerably from v.0,2 to 0,3)
http://drpetter.se/project_sculpt.html