I've found a way to get above the nether.
1. Find a Place where the ceiling is only one block thin.
2. Build a Block three blocks below and place a Rail and a Mimecart on it.
3. Place a downward faceing piston below the bedrock and destroy the Rail.
4. Trigger the Piston so the Minecart is inside the Piston head.
5. Get onto the Minecart, get out, and you will be inside the piston.
6. Spam jump, and you will glitch through the bedrock.