hey,
It is possible to make a wall mirror. However, this can become complicated.
If the mirror is ONLY oriented at 90 degree intervals, you can use the example (mtlFX.wdl) with a simple modification. Just switch the view matrix so that it clips the x or y plane instead of the z plane (for the ground). If the vector for this is say (a,b,c) just switch it to (a,c,b) or (c,b,a) (It depends which wall the mirror is on). just play around with this and im sure youll get it!
If the mirror is at a wierd angle however, you must calculate new view clipping planes (you must do a bit of math, I can't help you there
)
-Mike-