Does the Partnership Agreement require the Partner to pay for such an expense?

If so, click the green "Where Do I Enter?" button and type "Sup" and open the Supplemental Expenses Worksheet.

You can fill manually fill out a Form 8829 (or create a temporary Schedule C to have the program help you with it) to determine what the Home Office deduction is, then enter that as an expense on the Supplemental Expense worksheet.