Insulating hard to reach rim joist area

I'm in the process of insulating the rim joist areas in my basement. I'm gluing 2" XPS to the rim joist, spray foaming around the perimeter, and covering with rock wool. However, along one wall that runs parallel to the joists, a joist is placed so that there is only about a 1/2" of space between the bottom of the joist and the mudsill in which to insert insulation into the cavity behind the joist. Currently there is no insulation in this void.
One option I considered was stuffing small pieces of fiberglass into this crack until it fills up. This would be tedious and would not provide a vapor barrier.
The second option was to drill holes into the joist and inject spray foam into the void through these holes. The downside to this method, I would be doing it blind and couldn't tell if/when the void is filled. I'd also do it in "lifts" so that the spray foam could cure.
How should I deal with this issue?

 

I had a similar situation. I ended up cutting thin "slices" of rock wool batts and stuffing them in the area. A couple of thin sticks worked reasonably well to move the slices around to fill the space. I overstuffed it compared to the ideal, which reduces the r value a bit, but I reasoned that was better than voids. The advantage of rock wool for such an area is that it is not damaged by a little condensation that may occur due to lack of vapor barrier and will gradually dry to the inside assuming the interior humidity is reasonable if it does get a little damp. It's been 4 or 5 years now and no observable issues. The insulation has stayed put and there is no evidence of moisture.

 

Thanks, that sounds like a good idea. I have a lot of rock wool scraps I can use for it. The house was built in 1986, and I assumed the area was insulated with fiberglass batts, as I could see them sticking out of the 1/2" space. However, once I began removing that insulation it became obvious that the builder had just stuffed a small amount into the crack to give the appearance it was fully insulated. Luckily there is no sign of moisture damage in the void.