I'm afraid I can't take credit for this one...found it in a magazine once...
Cost: <$5.00 (plus shipping)
Item: Master Lock model 517D
Here's the scoop...
Pick up one of these Master Locks. They are the old school u-bolt/shackle locks that most of us had for our bikes way back when.
Here's the lock:
Take the u-bolt part and place it over your clutch and brake pedals:
Then push the lock side onto the u-bolt. it'll have enuf space to click once or twice:
There you have it...
When you try and press either the brake or clutch the other goes down with it.