I needed to convert my other pole to tubeless, and by chance realised that a JG 1/2” pipe end fits the Xtreme 22 (and probably many others) like a glove.
Just need to finish off drilling the hole through the middle that is already present using 8mm bit. The pole hose fits snugly through the hole. Put on you male rectus fitting or whatever, ‘o’ ring it on. Job done.
They cost 64p from Gardiners or you can buy the original from Exceed for £5
HTH somebody.