Flattening Baltic Birch plywood table top

I am making a Dutch Pullout dining table as described on page 56 of Tage Frid Teaches Woodworking (Taunton Press). The main top is 40” by 60” including walnut edges of 1-3” width (varying due to curvature of the edges) which are splined into the 3/4” Baltic Birch core. It does not yet have my (1/16” thick) shop-made veneer applied to the top or bottom which will be vacuum pressed. The walnut edges are more than esthetic: they keep the plywood flat. Hmm.

Now that the edges are glued in place, I measure cupping of the top parallel to the 60” axis of about 1/16” from the center to each long edge. This would not concern me as I would expect to draw the top flat in attaching it to the apron of a standard table. However, a Dutch Pullout has a floating top (which lets extension leaves to store under it). Thus flatness of the free top is important. I hope you can help me find a solution to flatten it. I have wracked my brain and have a list for you to ponder.

1. Live with it. Perhaps there will always be a bit of movement and that is OK. Perhaps any fix will result is more movement eventually anyway.
2. Flip it so the cup can relax on a flat surface.
3. Clamp it to a flat surface to train it. (Tried, not much success)
4. Apply moist heat and clamps to bend the plywood.
5. Plan or heavily sand out the high spots. Sand the leaves to match the thinner main top thickness. (Whew!)
6. Cut relief grooves on the top and bottom surfaces parallel to the long axis. (Spacing? Depth of cut?) Clamp it flat. Fill the grooves on top with epoxy. Flip, clamp flat, and fill the grooves on the bottom with epoxy. Sand flat. (Whew!)

If you could reflect on the best option or suggest another fix, I would very much appreciate your reaction.

By the way, adding to the challenge: I am building this in Ohio, but it will go to my daughter in HUMID Seattle. God bless wood movement.

-- Tod, Powell Ohio