Manipulating the projection matrix

hello guys

i want to manipulate the projection matrix that is used by opengl. Since i'm a noob in math i don't know much about matrix calculation, so i'm hoping to get help from some cracks here. The goal is quite simple and is described in the attachment: the picture shows a cube, viewed from the front, in parallel projection mode. the projection matrix should transform the visual data, so the top face of the cube becomes visible, too, while you're still looking exactly to the front of the cube (no rotation to the cube or something).

i assume, this is possible mathematically, right? if so, how does the corresponding matrix look like, and how do i use it within the engine?

I did some research on the web and found out, that what i want to do is called oblique projection, where the angle is 90 degrees (see attachment). The picture is taken from the pdf attached, which contains some math that i don't really understand.

I also found this article, where someone's trying something similar (just with opengl, not with jME), but hasn't got a final solution:

can anyone help please? :?

I don't think anybody here has any idea on how to manipulate the projection matrix. You might want to try posting on the OpenGL or forums. Also consider that jME usually generates the projection matrix for you based on camera parameters, you may have to hack around to make it use your modified projection matrix.