Is there some guide I can use for cooking soft boiled ostrich eggs?
Good question. It's probably not possible to dump it in boiling water for X minutes and end up with a boiled egg. It's just too big, I would suspect that you would end up with a yolk that is hard on the outside, and cold in the middle.
Which deals with Sous-Vide techniques for hen's eggs. It appears that the perfect temperature is in the 144 - 145 F range.
I'd try a sous-vide at 145, for several hours. You're going to have to experiment a bit.