Not possible. With the online version of the program, one account, one return. but you can create up to 5 accounts per e-mail address. Simply log out of the one you're using now and click the "create account" link under the password field.
Online Vs Desktop
Online version: With the online version of TurboTax (any flavor) you can only create one tax return per online account. But you can create up to 5 accounts per e-mail address. With the online version you will $PAY$ for each tederal tax return that you "print and file" or e-file. You will also pay a purchase price for each state tax return program, and then you will pay again to file that state return, regardless of weather you elect to "print and file" or e-file the state return.
Desktop version: With desktop you purchase the FEDERAL program one time and install the program on your computer. Then you can create as many federal tax returns as desired. But per IRS limits, you can only e-file a maximum of 5 federal returns. After the 5th federal return, you can print, sign and mail any additional federal returns. You DO NOT pay to e-file federal returns, or to print and file federal returns.
For state taxes, you have to purchase each state program separately and install the program as an add-on to the federal program. Then you will pay again to e-file the state return. You can avoid the cost of e-filing a state return if you instead elect to print and file the state return. With the desktop version only, there is no additional charge to print and file the state return via mail. There is only an additional charge if you elect to e-file the state return.