Decided on a direction with the fitting, though it was a fair bit of extra work so not totally happy with the solution. I am also now discovering some oversights with the design of my mould and the whole process of making this part. I had planned on putting the two halves back into their moulds untrimmed to bond them together, as this would allow me to exactly align them, and the excess material would protect the mould from the adhesive. Given that my solution for the fitting meant the one half would no longer fit back into it's mould anyway, so that plan sort of went out the window; I also did not account for the extra thickness that the fabric on the flanges would give me, and when I put the two parts together they are now actually 3mm bigger than what they should be. Unfortunately this is critical, as the part needs to fit inside silicone joiners which have an ID of 3.957". If I were to bond them together like this, the part would end up not fitting into the joiners and would be totally useless. What I should have done was made the moulds 2-3mm SMALLER than the final part size that I wanted, to account for the fabric going onto the flange area. 

What if I bonded the fitting in from the inside using the epoxy adhesive as I was planning, and then put 2 carbon strips over the back of it to give it some more surface area and support, and vac bag it. As it's not threaded on its bore, I would then be able to drill out the hole from the carbon? If that makes sense?