Actually, it's easier than that. This is my plan.
1. Pull out the speedo gently. Reach under the dash and disconnect the speedo cable from the back.
2. Tie a piece of cord to the end of the speedo cable.
3. Pull the cable out from under the car. Tie the cord to the new cable end.
4. Use the cord threaded through the center tunnel to pull the new cable back in.
No interior removal involved. If this doesn't work for me, I'll be sure to come back and curse a bunch for ya!
-Rusty