hmmm bummer bout your thumb, it seems that the thumb is mostly used to brace on the back of the neck so it seems you could learn to adapt to playing without youtube shows plenty of disabled guitarists, even one handed ones.

perhaps you can use think strings and tune down to make it easier to fret without the brace, or even play with the guitar down in your lap face up like Jeff healy
http://www.youtube.com/watch?v=ikHI7_PMFNc

that would allow you more pressure

you can definitely do it if you want it enough