A mixture of Damien’s response and your example number 2 worked for me. I used a simple login page to test, I expect that your registration view is similar. Damien’s response almost works, but is missing the sessionid cookie.
I recommend a more robust approach. Rather than manually entering the cookies from other requests, try using curl’s built in cookie management system to simulate a complete user interaction. That way, you reduce the chance of making an error:
$ curl -v -c cookies.txt -b cookies.txt host.com/registrations/register/
$ curl -v -c cookies.txt -b cookies.txt -d "email=user@site.com&a=1&csrfmiddlewaretoken=<token from cookies.txt>" host.com/registrations/register/
The first curl simulates the user first arriving at the page with a GET request, and all the necessary cookies are saved. The second curl simulates filling in the form fields and sending them as a POST. Note that you have to include the csrfmiddlewaretoken field in the POST data, as suggested by Damien.