If you're an administrator and assisting a PI with a grant you can add publications to PubSpace that are associated with a specific award. You can do this by creating an NCBI account.
Select C on the ABC list and scroll down to California Institute of Technology.
Enter your IMSS credentials
Once you've done this you can revisit the Manuscript Submission Page again. When you select Publishers and Others, this time you'll be taken to your unique account. On this page you can use the blue button to Submit a New Manuscript.