Does your ochestration care if the DB update is successful? If not, can you code the external assembly either spawn a thread or another process so the orchestration can continue on?
Is there any way to trigger the report generation outside of BizTalk? We have a system that does something like this. Every 5 minutes a service checks to see if there are records in a table. If there are it generates and sends emails based on those records.
The prolem with external assemblies like this is you are dragging BizTalk into other processes and is part of the reason you should avoid calling heavy processes from BizTalk. Try as much as possible to break up this big synchronous process into smaller and possibly asynchronous pieces.
Not sure if any of this was any help or not, but hopefully it gets you thinking 🙂