My method.

Support the ends that you want to feather with a good hard straight flat piece of board. Clamp well and plane all in one go to ensure a common bevel to all planks. As long as the ends are supported well and clamped well the rest of the ply sheets can be held up any old way, Preferably rising above table level rather than falling. This ensures tht the layers of ply are nicely compressed at the cutting edges. USE A VERY SHARP PLANE. (pic below)

For gluing up. Once again, concentrate on supporting the joins for a number of feet on each side of the join very well and very flat. Set the joints up perfectly, one above the other (no glue at this stage). You can glue them all in one go.

Now clamp the boards firmly (G cramps Not Spring clamps) both sides of the joint but about THREE FEET back from the joins on each side. This allows you to separate (raise) the ends of the ply planks (eg: with lengths of strips on edge or some such) enough to enable you to apply glue and wax paper as necessary to all the scarfs without having to readjust the planks once glue has been applied. Simply remove the spacers and allow the planks to fall back into their perfect alignment on the table.

Then choose a plank with a little natural warp in it and clamp it bowed side down accross the joint. I then add an old battery from a lorry to add preassure.

NB it is important to clamp the planks AT THE POINT MENTIONED IN CAPITALS ABOVE well. If these clamps are not tight the scarfs will slide away from each other under preassure when they are lubricated by wet glue. You may not notice this as there will be wax paper and glue squeeze out hiding the view.

Try to judge your glue right. Using too much glue will just require extra sanding afterwards of your already flat planks. DON'T FORGET YOUR WAX PAPER OR PLASTIC SHEET! between boards and the table etc.

I am sorry I do not have a pic of the glueing lay up. Next time I will take one.