We've workshopped this pose quite a bit in class, and the main focus I've found that works the best for most body types is attention to the lower body's alignment. Encouraging an inward rotation of the legs, big toes turned slightly inward even, and a sense of softness in the groins is key. If your groins are hard as you attempt to push your hips up to the sky, all you'll end up doing is dumping your center of gravity up onto the upper body. Now if you're really powerful, even with the groins hard, you'll probably make the lift, but it'll all be a muscling up, and it won't feel too nice. It should be a uniformed floating up of the body. So having fluidity in the hips to allow a bit of a recess in the hip creases is essential, I think.

If you don't like your hands by your ears, maybe it's because they're a bit too close to your head? Try them at mat's distance apart, see if that's any better for allowing the shoulders a touch more freedom. Have you tried having your hands on blocks angled by the wall? The higher your hands are off the floor, the more that center of gravity is encouraged to come toward your lower body, which is generally stronger for most of us. The legs have the power, so use them! Just keep the rest of the torso nice and long and supple. Remember, this is an asana, not a feat of weighlifting.

I had a teacher (Iyengar teacher, in fact) show us a very interesting technique once in how to get up into wheel WITHOUT the crown of the head first coming onto the floor. We set up in bridge first, heart arching up and groins and tailbone sinking down as always, then did a side-to-side swaying action with the hips to come up. Almost like we were stepping the body weight first onto the left hip, then the right, then back and forth again, in small increments, until we were completely arched in the pose. It felt completely effortless coming up that way! Of course you needed to know the basics of engaging the shoulder blades into the back, lengthening the torso and keeping the thighs parallel as you did that swaying-up motion, but man, it was amazing!

But from the basics, do practice bridge first, and practice it well. Work on keeping the thighs in truly parallel and the lowback long and open, as well as feeling the backbend up behind the heart, like there's a hand there gently supporting and lifting you up. I actually encourage my beginning students to let the hips hang heavy a bit so as not to take away from the feeling of the heart rising up and to the chin. Also work the backbends that Purna recommended to teach the body what it's supposed to feel. When I'm in a truly open wheel pose, my wrists feel no pressure and I have a tremendous sense of freedom in my heart and throat. And I have tight shoulders as well.