When I did mine, as per Mike's (b16sir) suggestion, I went to Home Depot and got a plug that was a believe a 7/8 or 3/4" nylon locking plug and used it RTV'd in the stock grommet. Its a tight fit and looks great. Other than that, I believe Honhon used frame plugs off a GSXR1300 or 1000 as you already mentioned. But the process is simple, after you remove the hatch trim, the whole wiper motor is bolted in with 3 or 4 bolts, from there, you remove the electrical connections the whole wiper motor comes out after the arm has been disconnected from the outside with a 13mm nut I think, might be a 15mm. But everything pulls right out and from there, you run a bead of RTV around your plug that you've found and pop it into the hole that the arm went into. From there, reinstall the hatch trim while your waiting for the RTV to dry and after that, powerwash your car at a car wash and check for any water leaks or anything.
FYI: The Nylon locking plug I bought looked just like this -
And I think it was like 58 cents. They are white from the Home Depot, and I sprayed mine black with some paint. Looks so much cleaner in my opinion.