Enter the used motor casing...
What you do is slide the used casing into the engine mount, with the nozzle pointing towards the front of the rocket. Screw on the retainer, and then push the 13 mm display stand up into the motor casing - this will give a very snug fit and hold the rocket upright nicely.
Et Voila! Rockets like the Illusion can now stand tall on the shelf.
|(Click to enlarge)|