Thanks for the reply! But i've taken a lazier route to solve this problem.. for those who might need it:
I've created a surfaceView on top of the qcar surfaceView, which min3d will draw to. I've struggled to get the models into the correct position on top of the rendered markers using min3d camera/object position vectors but with no luck, especially using the modelview matrix from native code. What i've done is bypassed the min3d "convenience layer", if i can call it that, and just went directly into the Render class, and replaced the object draw code:
_gl.glTranslatef($o.position().x, $o.position().y, $o.position().z);
_gl.glScalef($o.scale().x, $o.scale().y, $o.scale().z);
(copied from imagetargets.cpp)
_gl.glLoadMatrixf(projectionMatrix, 0); // projection taken from imagetargets.cpp
_gl.glLoadMatrixf(modelviewMatrix, 0); // matrix taken from imagetargets.cpp pose
_gl.glTranslatef(0.f, 0.f, objScale);
_gl.glScalef(objScale, objScale, objScale);
(dont forget to comment out push/pop matrix calls)
And it worked! min3d now renders the 3d object correctly on top of the marker. This is a bit of a hack, but it can be edited into something prettier, which I don't have the time to do. The app performance is acceptable (probably because i'm using a Galaxy Nexus) so I'm happy.
Hope this helps someone..