How do I do an itemized Delaware return while doing a standard deduction federal return?

In the federal section, enter all of your itemized expenses.  Then as you walk through the state section, when asked, answer that you want to itemize your return. 

The DE standard deduction is $3,250 for most filing statuses, and $6,500 for Married Filing Jointly, so if your total itemized expenses are greater than that, then TurboTax should prompt you to claim the itemized deductions for your state.