Does one have to control a significant number of nodes to disrupt a lot of transactions?
No need to have even one node.
The stress-test is paused right now. You can see the statistics and network health here:
http://statoshi.info/dashboard/db/transactionsThird chart "Transactions Accepted vs. Rejected"
Statoshi has so many charts, I forgot to check it for that one, thanks

So it's confirmed, when I made my transaction, attack was still ongoing.
Without a node with modified code how does one get around to doing what you're doing in an automated way?
Also, a follow up question, what are your main reasons behind this? Are you doing this to prove a point, like with the transaction spam attacks?