If you use Blurb it might be better to adjust the brightness of your monitor to match one of your books, and then use that as the guideline for adjusting your images in the Lightroom. But to create the preset, just set the tone curve the way you want it and then create a new preset. Give it a name, and make sure that only the tone curve is selected.
My question is how to create the preset? I can't find the mechanism to turn a tone curve in to an export preset.
To my knowledge, there isn't a way to create an export preset. You can apply presets during import, but I don't think that is what you want. One thing you could consider would be to create a collection from which to create your Blurb book, and populate it with virtual copies. Then you could apply the tone curve to all of those virtual copies and design your book. After you have ordered the book you could then delete all of the virtual copies and the collection.
You cannot add any editing work to an export preset.
For this, you would need to setup a development preset that contained only the tone curve. Unfortunately, this assumes that none of your photos have any tone curve adjustments already applied since development presets replace the old values instead of being additive.
In the library module, you can do "quick develop" edits that are additive.