Hi Elle,
Your post made me think... we have a 2nd electrical box on our house - it was there when we moved in, and that's where the hot tub is wired to. I just wanted to mention to you that ours is on the outside of our house - it's a 200 AMP panel outside. There is a 100-AMP breaker that links to the panel inside of our house. The things that are hardwired to the outside (200 AMP) one are the heating/air, stove and the hottub.
I just wanted to tell you that, in case there was a chance that your electrician could implement something like that, and save you the drywall work! We have a basement too - and the line comes in under the stairs, which is a big storage space that is not finished.
Maybe that could help...
Jodi