So you're gonna tag the south (gone bad) sister? Well, if you're beyond the skill level of rock walker, the North Rib is fully recommended to add some perfectly fun scrambling. This short, but mentionable route will get you there in style.
Once atop the real North Sister look to the South, the prominent rib is easy to spot. Head SSE for the South Sister and aim straight for the rib. Enjoy the views and imagine the old mining days.
Literally follow the rib-top. There is plenty of good rock to scramble. Don't forget to enjoy the views and check the weather. The entire length of the rib is probably only 15-20 minutes long and time flies when having fun, so enjoy the solitude.
Shoes, water. Hands are nice, but I'm sure there are some talented disabled folks out there who can get along fine.