I have a female Sargus which is hard to place as between S. cuprarius and C. irridatus. The text in the Soldierflies book accepts there will be problems and identification can be confirmed only via the genitalia. When I examined this female she proved to have a clutch of six eggs in the end of the addomen. Apart from i/d, therefore, I'd welcome guidance on whether by careful conservation I could keep the eggs viable through to the adult stage.
S. iridatus is by far the more frequent of the two species, and since the wings appear to be mostly clear that would also suggest S. iridatus. It should still be possible to dissect out the furca and confirm an identification that way (and I'd be happy to look at the specimen if you wish to pass it on).
I'm not aware of anyone who has successfully reared Sargus from the egg stage, only from larvae that are already well grown. Which is not to say that it can't be done, and it would be fascinating to give it a try! I imagine that the challenge will be getting the right moisture levels and the correct balance between providing decaying matter for food without the eggs/larvae themselves starting to decay. Sorry I can't suggest anything more helpful.