Preventing Infections Via Removable Media

Assuming a properly isolated/airgapped secure box, is there any truly secure method by which incoming data can be moved from an Internet-connected computer to the secure box using removable media without risking infection by sophisticated stealth hacks?

Some time back, I assumed as a thought problem that it would be possible to export the carefully extracted data as text, print (or photograph) it and OCR it into the secure computer. As it turns out, my bright idea is exactly what some intelligence agencies do, but it is an onerous process that would only be practical for small files, say communications cyphertexts.

Considering that jumping/hacking air gaps is reputed to be the current #1 priority among COMINT agencies and their contract researchers, has anyone determined a method by which any form of removable media can ever be reliably secure for data transfer to an airgapped box? I have some rough ideas, but I thought I'd ask the pros first.

Thanks for any info, links, etc.