How to improve contact between non-flat pan and stovetop

I have one of those pans, and I also have a glass top electric stove, and the answer is that you can't use the pan on the stove. Not only does it not make good contact, an electric stove is incapable of the rapid temperature changes you need for proper paella, particularly the blast of heat at the end to make the proper socarrat (brown crust).

I recommend that you instead get a portable butane stove, like the one I use, and use that for your paella-making.

I did some experiments testing how badly uneven the heat would be without interventions using flour. Answer: bad.

I ended up raising the pan up using a metal grill, and inserting pieces of aluminum foil to reflect and reduce the heat in the areas with too much browning. It is not perfect--the hotspot was still there, but much more spread out, and the result is that you also lose a lot of the heat of the stove, but it was still enough to sauté and rapidly boil broth.

Here are some photos showing the process.

There's no way to fully rescue it, but you may gain some performance by placing it on a carpeted floor & standing in it. Some judgement/guesswork/experiment will be required, else you will have to turn it over & repeat.

Put a towel or similar inside it so you don't get it dirty, of course & something on the floor.

It's not a perfect solution because once the pan base has bowed, it's always going to be too big for the rest of the pan surrounding it, but if you're lucky you can get a rough approximation.

Personally, I've been doing this with cheap pans for decades, usually to fix oil pooling badly, but I've never needed 100% accuracy because I'm on gas.

BTW, screwed-up aluminium foil is going to be a lousy heat-exchanger, probably worse than just the air gap.