YES it has been done... I did it... and here
is a write up of some one else... although I did mine for even cheaper than his... I took a piece of 16 guage steel and cut it to the shape of an oval filter to make both a top and bottom for the air cleaner, I then cut two round hols in the bottom plate for the stock carb boots to breath through, and one hole for the breather hose. total cost of parts was $16 bucks... I will look for the part number on the filter in the AM... its in my garage some where.
Product Line: NAPA Small Engine
Part Number: SME 708355
Features & Benefits Meets Or Exceeds OEM Specifications; Made In The USA
Warranty 2 Year Limited on Manufactures Defect in Material or Workmanship
Attributes Air Filter Bottom I.D. (Inches) : 8.75"
Air Filter Bottom I.D. (mm) : 222.25 mm
Air Filter Bottom O.D. (Inches) : 3.75"
Air Filter Bottom O.D. (mm) : 95.25 mm
Air Filter Height (Inches) : 3.25"
Air Filter Height (mm) : 82.55 mm
Air Filter Length (Inches) : 5.5"
Air Filter Length (mm) : 139.7 mm
Air Filter Style : Cartridge
Air Filter Width (Inches) : 2.75"
Air Filter Width (mm) : 69.85 mm
O.E. # : 110132114
Original Equipment Series : Kawasaki