10 year old thread so none of the original guys may reply.
Basically, the turbulent airflow in that area is blowing forward. Like a pickup truck on the highway with the back window open. The doghouse covers the slider track but since the track is T shaped, no matter how well you get the doghouse to fit, the open areas under the cross bar of the T are going to be open for a draft of air to blow forward into the aft cockpit.
The idea is for the white delrin block to sit on the track and do a better job of plugging up that hole. Because the canopy skirt pops up when open the block cant just be attached to the skirt. When you open the canopy, the aft frame slide pushes the block aft with it, and the lanyard is to pull it back into position when you close that canopy again.
Here's a picture of mine when I was working on the skirts. Fiberglass skirt, but the same idea as the aluminum doghouse. I'm still under construction and don't have a lanyard installed yet but without it, when I open the canopy, it pushes that block aft on the slider track where it would just stay forever because there's nothing to pull its back forward when you close the canopy.
The lanyard is just a piece of fishing line/fine wire/whatever works with one end attach to the block and the other end attached to the canopy frame to pull it back forward with the canopy.
Yeah, that drawing sucks. The thing you're interpreting as a hook it just meant to show a loose line.