I was a little concerned that the tape alone wouldn't hold it so, stripping some wire from the edges of my leftover aluminium sheets from TheMeshCompany (there was a 3 for 2 offer, but they completely puzzled themselves and sent me 4 for 2, which was nice!) and bound it tightly at the tip of the horn. From there, I wound it down to better hold the tape in place and to secure the feathers individually. It's made it much stronger, but more difficult for the next stage.
Milley15 the Milliner was able to provide me with these lovely feathers; Lincoln green speartips and iridescent green-black feathers. This bit was much more fiddly - getting the damned feathers lined up and shaped. In the end I used masking tape to hold them, as it's flexible enough to fix firmly to the back of the inner horns and to go 0-0-0-0 with two layers of tape around each feather stem to stop them coming loose and falling out. This created a satisfying frill around the edge, and helped stabilise the horns themselves.