Hello Yukui,
in theory you can use ncl to generate a file that complies with I/O API standards and is readable by I/O API library functions, but it is not at all trivial and requires an in-depth understanding of the I/O API standards. While there may be some initial learning curve, you probably will find it easier to generate the file by creating Fortran code that utilizes I/O API library functions or by possibly working with existing I/O API M3tools programs that are part of I/O API. You may also find this following discussion thread of interest and might want to reach out to the user to see how they solved their problem.