How much chain would you use and how do you connect the pipe to the chain? I was thinking of welding one link low on the back of the tooth, run cord through the link, then duct tape the ends of the cord to the leading end of the pipe!?
You would only need a couple inches of chain. I think you could just weld one link to the rear of the blade. As for attaching the pipe, what kind of pipe is it? Is it poly? If so you could create a loop with the chain and then loop the pipe through the chain and fold it back onto itself, then wrap duct tape around that. This would keep the stress of the pulling on the pipe and not on the tape.Another thing that might help is welding something sorta round to the bottom of the blade, so that as you drag it through the ground, it creates a little tunnel for the pipe to pass through.
Here's a picture that might help. It's from Toro, but the idea is similar. The only thing that would be different would be how to connect the pip to the chain.
Your picture reminds of when the "cable guy" layed cable in our yard. He used a vibrating device with a torpedo shaped piece of steel that led the cable. The cable was held by a loosely woven tube of nylon. I've heard it called a "finger trap" before. As kids we had a similar toy called Chinese handcuffs. A finger easily enters the tube, but won't pull out. I don't know if something like that would work for slippery plastic pipe or not.