Mine has an arm the has a knob to turn which holds it open. One thing you might try is cutting a one by piece of wood to the most open hieght you would want. Then cut some notches for a couple lower spots in case you to lower it some and still leave some room for air to come in. You will also need a slot for the bottom to rest on the frame of the hatch.
When a Woman says - Go Ahead: This is a dare, not permission. Don't Do It!