You would need to create a new account (UserID and password) for each return. With the Online version you can prepare one return per UserID and password. If you use the same account to prepare another return, then the second return would overwrite the first return.
The CD/Download product is a better overall value for people who prepare tax returns for their friends and family. It allows you to prepare and print unlimited federal returns and e-file up to five at no extra cost.