Buy an assembled Walmart bike, roll it out to the parking lot, roll it back in to the customer service center, and point out that it doesn't fit in your car assembled so you must return it or try to fit an unassembled box in the trunk. They'll find a box for you.

Someone at the Elk Grove Walmart knows how to assemble bikes so that they aren't deathtraps. Doesn't seem to be the only person working on bikes there, since we did have to hunt the racks for those that were ready to roll, but a tip of the hat to at least one assembler. The beater bike is aging fast but that's due to its components and not idiocy.