Reading further on this topic, it seems I should enter these office expenses under line 27a ("Other expenses") of Schedule C. However, in order to attach a Section 1.263(a)-1(f) De Minimis Safe Harbor Election statement for tangible property, TurboTax users must "dummy" it in through the Business Assets section even though you enter the deductions in business expenses, not assets (TurboTax says explicitly not to enter items already entered as expenses).
It would be helpful in future TurboTax editions to be able to include the election statement without having to walk through the Business Assets section.
