Bettas should be kept in AT LEAST 2 gallons, but if you dont want to buy him a new tank, you can try using plastic boxes (semitransparent)(something like this http://www.google.com.mt/imgres?um=1...2&tx=124&ty=82
) . I use these for 2 of my bettas, both are 6.5 gallons and they are much cheaper than any tanks and provide more room. They also reduce stress as even though light comes through, movement doesnt come through that much and they dont see thing that could scare them.
The two of mine who are in the boxes only have a heater and are doing really well. But if he starts to become more active you can buy him a proper tank so you can show him off to others.
I do suggest giving him some more room to swim, and for decorations try getting tall plants (avoid sharp plastic and wire) they have a tendency to hide and sleep in those.
And since hes scared easily it would be a good idea to put something for him to hide behind in his tank :3