Tim Low suggests making them into a fruit leather, and I think that Vic Cherikoff describes discarding the skin and then hammering the seeds to crush them and then drying the resulting mixture. But I'm not sure whether the seeds of all species would be safe for consumption, seeing as geebungs are pretty closely related to Triunia.
I get sick of geebungs very rapidly on long walks. The first few are tasty, but the flavour becomes cloying after a while. Don't smell them before you eat them, it's sometimes foul. My brother (who isn't the world's greatest geebung fan) has described them as being ripe when then smell like a mixture of vomit, wet dog and off milk, and less tasty than any of the three. The fibres attached to the seed makes eating them quite difficult. I can't see a way that they could become anything other than a bushwalking snack food.