are we talking about a wooden wall? cutting out a hole in that is easy.
if it is masonry, exterior wall, it could be a real problem
piano movers do this all the time, for instance
you need to think the whole process through, or allow a professional too do so.
other pertinent questions:
do you own the building?
how cooperative is the landlord?
how intrusive are government inspectors?
you can hire piano movers (as i have said) or riggers
you can also look into the cost & feasibility of disassembly of the flatbed, or, more to the point moving it on end
next question: if we move it on end, will you be able to corner?
you need to balance your expected needs, how much business you think this will generate, and how much you intend to add to the project for transport.
is it important enough to move or consider renting a nearby location with a wider opening?
my mind races with all the possibilities to solve a problem like this, the only thing i am sure of is no one ever said "i really wish i had purchased a smaller flatbed.
lets post a couple pictures, a drawing & maybe a little more detail. choose a reseller who would be providing service & ask to speak to their project manager. he may have many answers for you including do we void warranty by turning a flatbed on end? do they endanger their authorized reseller status by participating in such a thing?
i love a challenge, but sometimes every solution causes more problems than it solves...