Blowing cellulose through top plate

Master Brian

There is one wall along the front of my house that I am trying to find the best spot to gain access through to which I can blow cellulose insulation into. I have clapboard siding and the front of the house has a nice coat of paint that I really hate to disturb by pulling siding. The inside is wallpaper, so I'm not willing to mess that up by blowing from the inside.

I do however have direct access to the top plate through the attic directly above. I need to basically run a 1-1/4" hose through the wall to insulate. How bad of an idea would it be to drill a 1-1/2" hole through the top plate in this area. Along most of this run the top plate has nothing on top of it, so I could easily add a new 2x4 directly on top once finished. Is this a bad idea??