No, you cannot file multiple returns with one account online. You would need to create a separate account and pay separately for each return online.
So, if you have multiple returns to prepare, then it is actually best to use the desktop program. And, if you have no states, then you will not have to worry about the state e-file charge, which means you can prepare all your returns for the price of just the Deluxe CD.
Note: You can prepare as many returns as necessary, but you are limited to 5 electronic files with the CD program. Anymore returns would need to be paper filed. This is an IRS rule.