Randy (Radioflyer) taught me this trick last year at OBSKC.
Assuming that you want to do a counter-clockwise insane:
His approach is to fly the kite to the top of the window, then turn the kite to the left so you're starting to point the nose at the ground. Just before you've completed the 180 degree turn, sharply axel the kite using your right hand, then keep the right line taut while giving slack with the left. You're basically snagging the right line around the wingtip, and causing the kite to pivot around that line.
Don't forget to pull out before you hit the ground. Wait for the rotation to bring the kite around into something resembling the turtle, then sweep both hands back to pop out of the insane and fly away.
To do a clockwise insane, just reverse the turn and the hand used to axel above.
In normal winds, you may need to walk slowly backwards after the axel to keep the line taut. In light winds, you have to run backwards full-tilt.