hello edwardcox,
I'm not part of j-cook team but as far as I'm concerned I think that there is a security issue if you share your j-cook account. Doing this, the other person can modify or even delete all of your work with few clicks.
So, I don't think that's a good Idea.
On the other hand, I understand that you are doing a collaborative work with the other guy. This feature does not seem do be included right now in the builder. Maybe you can ask for a feature request
And last point, as this is a service, I think that's more fair for j-cook team that you purchase points for the second account. Since now, Jocelyn made a great work and the best way to thank him is to buy few points.
Regards.