lol give him a wallet that is really really secure and make him guess the password to it. Give him clues. Take a screenshot of a wallet with like 1000BTC or something.
When he figures it out, just have only 0.001 in it.
Lol.. that's so evil.
This might work, but if the picture said 1 BTC or something (1000 is unreasonable).
Have fun trolling your brother