The longer box we had was 57" long and our bike was significantly longer. The typical bike is prepared for shipping by removing the front wheel, pedals, and seat post. The rear derailleur is loosened, rotated, and taped to the frame, the handlebars are turned, and voila! it fits into a bike box.
Instead of doing the same thing for a single bike, I decided to shorten the bike as much as possible. I started by doing everything listed above for a single bike and ended up with about 75" of bike. I then removed the rear wheel and uninstalled the rear derailleur and taped it to the frame, all the while leaving helpful instructions for the bike mechanics to put back together, like "Sorry, lost the bolts. Hopefully you have the right replacement bolts to put together".
After getting everything uninstalled the bike ended up at 60". Three extra dumb inches. After wrestling with the bike, hoping for a miracle, I decided to cut a hole in the end of the box to fit the rear fork out. I put a block of wood in there and secured it with 2 pounds of duct tape, bubble wrap, scraps of cardboard, and more duct tape. It fit, and the bike box was only 65" long, which was under the magic 70" limit that doubles the shipping cost.
I finagled the seat posts, handlebars, fenders, rear rack, and other miscellaneous components in there and it weighed in at 58.5 pounds, which was under the other magic limit of 60 pounds. I added another pound of packing tape and duct tape, and we have a bike on its way to Portland.