Hello,
I just got a call from the CAcert folks. Unfortunately, right now, there is no way that you can create your own private key when being validated for an organization. The only option for the moment is that I, as organization administrator, create your certificate including the private key and send it to you.
The certificate then will contain your full name, your mail address @documentfoundation.org, "The Document Foundation" as entity name, plus your official role.
I promise to immediately delete the private key, but theoretically, of course, this would enable me to read mails encrypted to you. CAcert is working on an improvement of their process, but there is no ETA yet.
If you are still interested, please drop me a private message.
Florian