If you threw enough money at Boeing, I'm sure it could be done. But why would you make such a daft move? The standard upper-deck has more than enough space at it is; in fact quite a few B747-400SF conversions have put a bulkhead on the upper-deck as there is no need, at all, for all that space.
Try having a look at the upper-deck of existing B747-400Fs and you'll find most operators have a rather sizeable galley, between 4 and 8 business-class seats + bunks for between 4 to 6 people. Really, what more do you need?
Getting people up the stairs from the main-deck is not any issue, getting them evacuated in case of an emergency would be. But that's not an issue either, as the door (there's only one; the LH
one is blocked) is fitted with a slide, which can be used as an inflateable and is, if memory serves me right, certified to carry 20 people - more than any 747F will ever carry.
Your idea is, I'm afraid, not viable.
From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove