I gotta be honest and say no, I haven't tried to make walnut look like laminate. I've stained laminate really dark to make it not so obvious that it's laminated.
Seems like it'd be a LOT easier to just find a walnut butt to go with that forearm...
perhaps Boyd's would gen-up a walnut thumbhole like your laminated one to go with the long forend.
Or,.....paint them a matching color.