Try it please :)
I've spent several hours around this option.
I've explained above why it cannot work, but I'm still digging on alternative that wouldn't consist on revealing the private key.
More feedback, if I understood it right: if you extract the findNonces function, dump the 1500 files of 512 bytes, transfer them to a machine that has the ssh private key, then you should be able to sign without risking anything (encryption is RSA-OAEP), because your private key wouldn't touch the software.