Esther-
If you have (or have access to) the PHP skills (or can make a suitable donation to LimeSurvey and find a developer who has bandwidth), adding Nanogong shouldn't be too hard. You would probably want to store a binary file, so you'd need a BLOB datatype, and none of the existing question types use that. So, you'd need to create a new question type to store the BLOB. I had to create the Equation question type a few months back, and it only took a few day's effort.
However, a lot depends on your timing. We're nearly ready to release version 1.92, which (knock on wood) will be the last in the 1.xx series. We're also nearing release of 2.0 alpha, which uses an entirely new framework. So, if you need something soon, you'd need to use the 1.xx approach, but it would need to be ported to 2.x. If you can wait about 3 months, it might be possible to build it directly into the 2.0 branch.
/Tom