What exactly is the plan? Just going to place the mini netcup into the 5" cup I presume? Trying to remove the seedling from the cup will probably hurt he roots, which will likely be tangled around the cup by then.
Be very careful when you do it. The roots.are ultra delicate at such a young age, and the hydroton can sometimes be clumsy to work with. Try to be really careful when you drop the roots in there... hydroton rolling and shifting around on you could be a potential problem. It would be a good idea to devise a way to build a wall, or perimeter around the transplant location. Perhaps a large 3" diameter pvc pipe cut to a length of 2" or so would make a safe little 'island' I your 5" netcup to drop the babies in. Then just remove the pvc cylinder and the hydroton should just shift right into place.
The first time I transplanted into hydroton was a fiasco. Didn't anticipate it to be so awkward to work with, and roughed the girls up a bit. One of them ended up badly stunted. I found Rockwood cubes best for seedlings, and just drop those suckers into the big netcup once the roots pop out bottom. Maybe next time