Better yet: if the top of the stack is (say) Sawmill, Clay Mound, Colliery, you can use the Construction Firm to build the Sawmill and Colliery as long as you buy the Clay Mound for two francs in the middle of that action. The Buildings Overview description of the Construction Firm is very clear about that. I think you could even sell the Sawmill to get the money for the Clay Mound, though my copy of the rules is less explicit about that.
Interestingly enough the iPad app won't allow this. One of the players in last year's WBC final (the winner, in fact) used the construction firm to build the Arts Center, sell the Arts Center, buy the Black Market, and build the Colliery. I ran the event...and allowed it because (1) I didn't see anything in the rules that explicitly state you couldn't do this, and (2) the player in question had other buildings he could sell and likely would have done so if necessary.