hello melonfish!
i make flukes as often as i can, elder is the best for making them round the campfire as no carving is involved. i use a very long flat head screwdriver (thick head, thin body) to remove the pith usually. i clamp the screwdriver down vertically with the end up then sort of pretend to make a fire by friction, because of the thin body it can go round slight curves (i love curved flutes) and makes for a very clean bore. don't worry though if you cant get it all out, as long as there is clear air flow it makes for a very soft sound with an eneven bore.
not long off finishing part 1 and 2 of my flute tutorials, the second part is an elder (or bamboo) flute. if you get stuck or can't get a sound let me know and ill do what i can to help.
good luck, when you get a flute that works and get it sounding i guarantee you will love it. nothing as hauntingly beautiful as the sound these flutes produce drifting through the woods at night!