Willie, Imagine a plank of hardwood planed smooth, or it could be multiple thicknesses of hardwood ply glued together, which would be more stable. Dimensions 2"(3" would be even better, allows for wider laminations and gives more bearing surface so the plane wont tip) x4" tall as long or a little longer than your intended bow. On the top edge saw with a dado head or rout a groove wide enough for the lamination. Depth of the groove is dependent on what type of lamination you are cutting.
If you wanted a form for a belly slat you could make the groove 3/4" or 7/8" deep. If you wanted to do a core lam it could be 3/16"-1/4" deep.
Mark out the handle/ dip area on the top of the form. From the ends of the board, up from the groove mark up 3/8" if you want to do a belly slat. Connect a line from this point back to the end of the handle area. Repeat for the other end of the form if it is for a full length stave. Saw off this waste, and you have your form. Run a strip of frictionless tape down the each side on the sole of your electric plane, trim the excess from over the mouth so depth of cut can still be set.
Place your belly slat blank in the groove. It could be fixed to the bottom of the groove with double sided tape , or held in place by screws on side, through the walls of form. Just the tip of screw would bite so the slat insn't comprimised.
Set the plane for a fine cut, no deeper than the thickness of the frictionless tape, so the planer won't cut into the form.
Run the plane on the slat as many times as necessary until the taped part of the sole bottoms out on the form.
Hey presto you should now have a belly slat with a flat section as long as the handle, or fade area, 7/8"deep tapering to 3/8".
If you wanted a form for a core lam, you could use 3/16" or 1/4"deep for the groove, tapering to 1/16" or 1/8".
My method gets around you needing to add a powerlam under the backing lam, like you often need to do if you use thickness sanded taper laminations. You can still glue on a handle riser if you are making a deep narrow handle, it won't pop off because the flat area gives you enough thickness so the dips won't flex.
My proposed form isn't very adjustable but minor variations could be achieved by placing a thin parallel lamination of sawn or planed wood on the base of the groove before placing the blank on top.
