I guess I'll have to use a GBAK wrapper, or, just use the default page size that gets assigned by the FB service, which I think is always the 16K page size, which is what I want 100% of the time anyway.
According to the Firebird docs, the default value is 4096:
Optional Parameters for CREATE DATABASE
Optional PAGE_SIZE: Clause for specifying the database page size. This size will be set for the primary file
and all secondary files of the database. If you specify the database page size less than 4,096, it will be changed
automatically to the default page size, 4,096. Other values not equal to either 4,096, 8,192 or 16,384 will be
changed to the closest smaller supported value. If the database page size is not specified, it is set to the default
value of 4,096.