I used any holes in the mars for haliards etc to poke a stick in to hold the conduit against the side the. Drill and rivet. Once you get one in then it should be easier to get the others.
I have often wondered how mine was put in as there are loads of stainless lacing eye type things well away from useful apertures, maybe a factory jig.
I'm just about to put a replacement RG8x cable up my mast but the old cable was exactly 5mm any one know how to enlarge the holes without removing the old cable as I need to use it as a draw cord?