That's often the case with shows unfortunately - in fact I don't even take a camera to the NEC classic show because there just isn't going to be any opportunity to get a decent shot. And it's remarkable how few people will hesitate to walk in front of someone who's clearly trying to take a photo - so much so that it's a surprise when they notice and wait for me to finish.
If you have trouble getting a shot from lower down, you might practice with holding the camera at waist level - line the shot up normally, then carefully lower the camera body while trying to adjust the angle to keep the subject in shot. You'd probably need a fair bit of space around the subject to take into account getting the angle a bit wrong, but with practice it might be do-able. I remember watching pros at some event shooting by holding the camera body above their heads and just hoping they'd got the angle correct, but I think I also remember being able to buy 90° viewfinder adapters that also might help, if you can find one suitable for your camera.