Your 5 foot snake still has plenty of time to grow out of a 55 gal tank. No need to worry about that. For the shelf thing...The shelf Will not help him lift the lid, he would have done that already if he could have or really wanted to. A 5 foot snake is a lot of snake and much taller than the tank thus, leverage is on his side so...What you could do is put a nice heavy branch in the tank and the snake will love you for it. chances are it will turn the branch into his new bed. Note: Make sure the branch will support his weight. If your not sure make a few phone calls. Good Luck.