I don't condone this obviously but you just need more of the transmitters and leave them near him. Everytime somebody nearby uses one of those my throughput drops a bit. It's never cut out however so you'll just be slowing him down.

My 802.11g signal creates a lot of interference with video senders. But as it's the unlicensed band and he's not modifying his equipment then he's perfectly okay to do this. You trying to jam his signal however would be frown upon by the authorities.

Also be aware of the fact that most video senders don't have a particularly strong output. They're normally about 10mW but a wireless LAN would be using at least 22mW. Don't know about cordless phones as all the DECT ones in the UK don't actually use 2.4GHz.