couldn't you just use a go between (middleman) pc?  so for example you create transaction on online pc, unplug that usb stick (usb #1), plug it into pc/device #2 (middleman pc), cut and paste the transaction onto a second usb key(usb#2 that never is used except between offline pc and middleman pc), unplug usb #2, plug into offline pc, sign transaction, plug back into middleman pc, cut and paste signed transaction to Middleman pc/device, unplug usb #2, plug in usb #1 (this usb only ever touches online pc and middleman pc), cut and paste signed transaction onto usb, plug into online pc and transmit.

hope that wasn't too confusing. i'm no security expert and have no idea if this is even feasible or would add any extra layer of security. it does add another third device and makes the whole process longer but if its only something thats done infrequently (to access a cold storage wallet), and it would work, might be an option.