I recently figured out how to solve that^ one with 100% the long way around. Idk which one LemSteven considered in the list but personally I like that way better.
[have a the last lemming going to the balloon, dig a whole for himself and the worker to climb up.]
Personally I think the designers left that back route in on purpose. I mean, come on, all they would've had to do is make the steel go up to the ceiling but they left a large space instead.