> What command or JDBC url switch should I use to turn ForcedWrites off via
> JayBird?

The correct way is to use FBMaintenanceManager class, there are an
appropriate methods for changing the DB configuration.

> What other optimizations would you recommend to speed up our tests?

"Doctor, I'm feeling not very well, what medicine should I take?" :)

There might be a plenty of issues, not necessarily related to the disk.
Without profiling the test suite it is hard to say anything. You might
play with buffers, but also a simple caching of prepared statements
improves the performance significantly. You might have issues with the
queries (bad indexes), or implicit datatype/charset conversions.

Roman