I install graphics on vehicles for a living, so I'm quite experienced in getting rid of bubbles. The only issue is that when I leave a bubble on a vehicle, I take a knife to it and gently poke a hole in it to release the air. I guess you wouldn't be to open to try that, so here's an alternative.
You need to people for this. First, you put two corners down straight and then, make sure you take your thumb to it to wipe down the complete edge while the other person is still holding his side of it in the air.
Next use something with a firm edge (like a plastic squeegee) and use it to wipe little by little the protective cover down. Hope that helps