>
> The fence could be made from a block of wood with
> a saw kerf for the veneer clearance.
>
> Does any of this make sense?
>

I came late to this discussion. Why would anyone want to cut veneer 
with a mat knife?  The correct instrument is one of those little veneer 
saws that have teeth on 2 edges. Veneer is usually cut in a stack with 
the veneer saw using a batten for a straight edge. The purpose of this 
is matched edges. The saw is ambidextrous. The teeth are sharpened just 
like you would sharpen a knife. As many soft strokes as is necessary 
are used to cut through the stack while the saw is held with the blade 
flat against a thick batten so the angle of cut remains constant. You 
can cut single pieces the same way.

  If you are cutting a single piece of veneer, you can also use a very 
sharp chisel that has been specially prepared for this purpose and is 
used for no other purpose. It is also held flat against the batten and 
used like a knife, or it can be used freehand for curves. This old 
fashioned method is worth learning.

Jim Thompson, the old millrat in Riverside, CA