As sparksd says, you can't. NMI is only an importer so you can't use it to export
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NMI does support writing to a flash drive. The author recently provided support for writing to NTFS-formatted HDDs:
Nexus Media Importer
This is exactly what I am attempting to do but with video from a Gopro. Which eats up memory cards quick.
I used NMI on a trip to transfer photos from my camera's SD card (using a card reader) to a flash drive (had to copy to the Nexus then to the flash drive).