I experimented with this with an H. Patellifera ooth. I sliced just barely enough off of the ooth to see if there was anything developing, and I did find nymphs inside. To seal it back up, I used glue. I put a little bit of hot glue where I wanted to put the ooth, waited until the glue was cool but still sticky, and stuck it on there. Except for about 5 nymphs, the whole ooth hatched. You just have to make sure the the glue completely seals up the ooth, so that it doesnt dry out.
Im not saying that this will work with every species, but it can work with H. Patellifera.
Thanks,
Andrew