Coincidentally, I am actually working on something that does that. It is not yet ready for the FEX, but I will remove the files here and replace them with a link to the FEX.
There might be several bugs in here, and it might not work for your specific case, but most of this code is compatible with Matlab releases back to 6.5, as well as Octave.
Run Untitled.m for an example with the built in example mri. Scrolling will scroll through the planes, dragging will change the window level.
