I love this. Is there a decent how-to with best practices for creating the private keys to work behind the hologram? You're releasing hundreds of these into the wild, this might be useful.
Currently they are meant to store the private spend key in base64 format. There is only enough space to store such a key of this size.
I do not know of a publicly released version of software that does this. Although there may be one that exists that I'm not aware of.
The alternative would be to store the hex version of the private spend key (half on one side and half on the other bit that may cause problems when attempting to redeem and get the hologram off of the paper insert.
Looks like there is time so I may end up releasing a version of my software that does this. But as of right now I can't promise that just yet.
As you can imagine just shipping these will take some time.
edit: On second thought you could use a site like
http://tomeko.net/online_tools/hex_to_base64.php?lang=en to convert the hex private spend key to base64.
I can't vouch for the accuracy of this site. It would be best to test the conversion and redemption process with a tiny amount of XMR to see if the conversion works. You could even do it on testnet so you don't lose any funds that matter.
Also be advised that using a 3rd party website could allow for keys to be compromised.
Do a test... Of course you could possibly load the page, then disconnect from the internet and input your hex string (generated from moneroaddress.org offline) to convert to base 64 then print it and close the page etc.
**Please be advised that I am not offering this as actual advice to use but more as options for those who want to assemble a DIY coin with the brass giveaway coin.