Ok, I thought you meant 1 or 2 cm towards the side of the rim.

Try a layer of Hockey tape, you can rip it to width pretty easily.

I dunno what else.

Wait, are you running fixed with no brakes?

Sometimes, the tube and tire will actually move (rotate around the rim) and it's ripping because the stem won't move with it. I guess it's more accurate to say the constant skidding/braking back and forth movement over that spoke hole.

Hope that makes sense.