Steve Hamlin
>As this is pretty much guitar back thickness, suggest joining by tenting between two rows of nails set just a smidge tight of the total width (won't need much sideways clamping pressure assuming the pieces are well jointed - candle the joints to be sure.) Run packing tape (plastic stuff) under where the seams will be, lay the outer two against the nails, with the middle two tented up, run three beads of hot hide, snap down flat then weight or clamp down the seams and wait.
If any of the seams are out of alignment, use a hot iron with a damp cloth to press them flat and reclamp.

If you're using cold glue for the veneering, can't see this affecting the HHG seams (though I haven't done this)
As further evidence that I haven't done the veneering - is relative movement an issue? Could be worth making sure the veneer is at least as dry as the substrate (bake it perhaps?)

Cheers
Steve