Actually, if you have enough August points (which you can get on the Hana route mainly), he is a rather safe option too. I do not see at the moment why you think this is not an option if Rosi is high proiority for you. Unlike Kate, Chuck or Killian, August does not want anything for his intervention from the start.You can also go to August, Chuck or Kate for the money to help Rosalind. Kate and Chuck are dangerous but August can be an option if you have enough points with him and Rosalind isn't the top priority for you.
When August states "I am very sure of it" when asked if "just Oliver" pressuring Rosi will take a step back, for a moment I awaited to hear an instrumental version of a certain Nino Rota song playing.
Outside Feli and August, Killian is a comparativly safe option too. His threesome demand is really unproblematic if Rosi has at least some libido points.