I've used subpar plugs before. You know, basically enough to snug up the headset. I've even tightened a headset with a long piece of all thread and washers.
It sure seems that with carbon, it will eventually get loose without the constant preload of a good and grippy inner plug. It was a big surprise considering I had steel and aluminum steerers with no plug that were fine.
I am unfamiliar with the fork. Do you need a proprietary stem or headset?