One thing you can do is to remove the bird board from outside. This will give you decent access to the top plates.
It's still tricky to drill but at least you are standing on a ladder, working at eye level instead of laying on you belly in the isulation. Sometimes there will be extra space from the original installation.
Use a sawsall to cut the nails and the bird board will usually come right out. Use screws to reinstall the board and you can remove it for future additions.
And....if you add circuits, make the wiring clean and neat like the original wiring, NOT like the added circuit on the last pic. It's not any harder to make it clean and nice.