Capturing input from a graphics tablet

[Jabberwock]

I have bought a cheap graphics tablet and I am trying to use it with games. While it works in some games, such as FPS and osu! (where it is great!), I also wanted to use it as a lightgun in MAME (retro emulator). However, it does not seem to work (i.e. it seems to work in menus, but is not detected as input).

I wanted to circumvent it with FreePIE (or any other software), but I have no idea how to capture that input. The device reports as a standard HID Graphics Tablet, but it seems there is no way to access the data it sends... Any ideas?