I don't think this idea stinks.  Pun intended.

TP with a business made renovations to a bathroom in his home that is used by himself and his clients.

Is this Qualified Improvement Property, 15-year property eligible for bonus depreciation?

Then, if you are flush with more ideas, how can business-only use be defended?   He claims it is only during office hours and his wife doesn't use it.  He has 3-4 client meetings per month.

Background:

Qualified improvement property (QIP) is any improvement that is Sec. 1250 property made by the taxpayer to an interior portion of a nonresidential building placed in service after the date the building was placed in service. However, expenditures attributable to the enlargement of the building, elevators or escalators, or the internal structural framework of the building are excluded (Sec. 168(e)(6) and Regs. Sec. 1.168(b)-1(a)(5)). The requirement that the improvement be made by the taxpayer means that taxpayers cannot acquire a building and treat any cost assigned to improvements made by a previous owner as QIP