I took the pattern (roughly) of the plastic cast carriers shown at the bottom of this page:
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Except I make it out strong cardboard. The point fly gets hooked into the hole in the middle with the point of the hook going into the cardboard. As I wind the cast on, the droppers can get hooked anywhere onto the cardboard (can't do that with the plastic version). Finally, I have a slit cut in from the edge of the cardboard and sliding the line end of the cast into that slit is enough to hold it with friction.
Easy to make. Cheap to replace. Very flat so lower volume than the pipe lagging method. Only disadvantage is that they go soggy if you drop them in the water.