I did say one could use "a calculator". Presumably, one could balance it being fancy enough to be able to handle EC math, while not being fancy enough that one had to worry about it storing ones key for a long time or getting compromised in some fashion.
The EC algorithm is actually fairly simple (see JackJack's pywallet for an implementation), but relies on bigints (arbitary percision integers) which may or may not be available on a stand-alone "calculator". As has been said elsewhere, this is an ideal application for a raspberry pi. You don't even need to connect it to the internet. Just download bitaddress.org from the github, transfer it to the pi via a memory stick (or load it onto the boot partition of the OS SD card) and you're good to go. Attach a printer, and your key has never been exposed to the outside world. You should reflash the SD card afterwards, to be sure nothing remains that can be exposed later, destroy it if you're paranoid, and the printer too, you never know what's stored inside the modern ones, but an ancient text-only line printer should be safe
