My canoe project (early 1900s Maine guide canoe, unknown builder) has about 1/2 inch of hogging. It presently has all ribs and planks repaired, and inner and outer gunwales in place. So basically a complete canoe without canvas. I hung it upside down in my garage over the winter, suspended from the two quarter points. Then I added an additional cross bar under the center of the canoe, and tightened those ropes so the center support held all the weight. After 4 months of hanging like that, there was no change in the shape of the canoe. None.
So my takeaway is that something more drastic would be needed, such as the ideas earlier in this thread. But for now I will just live with it and focus on completion.