I'm a bit confused. Are you talking about curling your thumb over the top of the neck to fret the thick E string? You say you can't hit the first string with your thumb, but that would be the thinnest string, so I'm not sure why you'd be using your thumb on it. I'm sure you know about Tony Iommi, of Black Sabbath and how he lost the tips of his fingers on his fretting hand. He made prosthetic tips and changed the way he played to accommodate it. Also, Django Reinhardt lost the use of his ring and index fingers so modified the way he played.