I used the cap off a Polycement tube to get the initial concave shape and then the end of a paintbrush , dipped in water to smoothe the interior.
I smoothed the inside out with a plastic plunegr from one of the kids Ibuprofen syringe tubes [whatever is to hand]. The fact is DAS is not an adhesive, like Milliput, but it doesn't need to be. I just needed to plug the hole and hopefully friction will keep it there.
With hindsight I could have used the spare Dark Talon jets inside, or got some Drop Pod Retro Boosters would have looked cool as it would have matched the four on the rear.
I also spent soem time stripping the bikes subsequently when separating one of the Ravenwing banners so I could reposition it standing upright it shot off into the man cave. Hopefully I'll discover it's hiding place at some point.
As you can see the stripping went really well, I was using a 59p Acetone FREE nail polish remover from Home & Bargain. it took just minutes to strip them, so no leaving them to bathe for months like Dettol.
In fact, I even did a video to show how quick and easy it is: