Why not run 17" wheels on all four corners? I have been doing that for over 10 years. Sure makes rotating tires possible.
Sure if you only drive 500 miles a year...
Most owners drive their smarts ten times that and subject their front wheels to potholes and curbs
I'd rather have 15" rims up front and not be able to rotate tires - cheaper than replacing a bent rim...
I run the EU 16" Front (175/50/16) -- 17" Rear (225/35/17) on one of the 450s and I had those tires shipped in from Germany (Four tires were $1000 shipped).
I'll put a guess out there that the 15" Front -- 17" Rear was designated 'USA Only' because the 16" Front tire size was never available in North America...