Your installation seems to be different than the one on Journey On. That's why a picture would help.
For Journey On, on the outside, the radar arch has round mounting feet welded on the tubing. These feet bolt onto the cabin top and have holes which gives access to the tubes.
On the inside the bolts pass through round backing plates. The forward backing plates have holes and access to the external tubes is through a hole drilled through the cabin top.
I don't know of any internal backing plates (if that's what you're talking about,) that are shaped like a scoop. The radar arch maker's name should be on the radar arch. Contact them. If the scoop just provides cable routing and isn't a backing plate, you don't really need it.
Otherwise, you can just drill a hole through another backing plate, up through the cabin top, through the external foot and into the tube through which you want to route the wire.
Boris