Basically it would work like this; Thelma is looking to pass a message to Louise, so she XOR's plaintext file A against random byte file B producing ciphertext file C. Now since Thelma works for an unethical company that like to read it's employee's E-mail, she's in need of some "plausible deniability."
Enter "One Time Pad Plus." Thelma now XOR's ciphertext file C with "Safetext" file D (any typically company approved useless memo) producing "pseudorandom" file E. She now copies random file B to disc and sends it to Louise via secure sneakernet. Then she performs a military grade wipe on A and B. Now she can send ciphertext file C via company E-mail.
If her message is intercepted, she has deniability, she can claim she has read of hackers, cypherpunks, and other evils equipped with packet sniffers, and being concerned about security is using encryption. She can then produce "random" file E and decrypt ciphertext file C which will yield not A but D the company approved useless memo.
Ok, I'm new to this crypto bit so I probably will have more mistakes here than correct answers. Anyways I'm going to give a shot. 1)If you have the secure channel(sneakernet) that you have to re-init each time you use th eone time pad, then this will be most likely a novelty, since Lousie could have slipped Thelma the plaintext when she slipped her the pad. 2)If you're using a pad like this, if I'm not mistaken isn't this what Kahn calls a 'book cipher' where it would be simpler to crack than a true one time pad that is truly random. 3)Thelma could have used stenographic technology to send the same information, she could have used faxes that when decoded could yield a message(kinda like the old punch cards) Anyways, this is just the view of a complete rank amateur. Give me feedback y'all. Ben. ____ Renegade academician. They're a dangerous breed when they go feral. -James P. Blaylock in "Lord Kelvin's Machine"