I found a solution, it's rather simple. Unzip the driver package, find the line AdjustPage = 0 and replace it with AdjustPage = 1. Then install the driver. Et voila, there is a third tab in the control panel where you can adjust the area the tablet gets mapped to. Don't ask me why the default value is 0.
Tested with MacrokeyManagerGeneric _V343_X64.zip and Aiptek MediaTablet U14000, should work with any other Aiptek/Trust tablet.