You are best shopping the problem around to a few fire engineering firms till you find one that has a solution you are willing to go with.
Different engineers have different appetites for risk. To overcome spandrel separation issues by way of an engineered solution, some will require sprinklers in every room others fire detection. There are others however, that will want the spandrel separation issue fixed at the problem…upgrading the spandrel separation itself.
Call a few firms, talk to the engineers, ask if they had similar projects and if so how did they overcome the problem and what was the cost.
Each solutions has its pros and cons, it could be higher engineering costs (due to risk or complexity) , higher installation but lower ongoing maintenance costs or vice versa.
Most Councils are happy to accept any proposal that comes from a qualified engineer when presented in the proper way (i.e. Fire Engineering Report/Upgrade Solution etc etc).