Thanks andyabc, i used the S.onyTablet.S [FLASHER] v3.0 and attempted to install Option 2 (4.0.3 R5A wifi only for Sony Tablet S) so all files were pulled down automatically by the tool. Everything went smoothly and i selected "FLASH R1A's hidden.img [last shell-enabled]", all checked out and the tablet rebooted before it got stuck.
Your solution sounds feasible but I have no ADB access so what would be the best way to find the SKU. Also, am i correct to assume that to use Condi's tool to sign the package I would need a working rooted tablet?
It sounds like there is no quick solution to this and I am flying out tomorrow. I guess I will attempt this battle when i return. Thanks again for the ideas.
For the second solution you just need a PC, device on Recovery and an SD Card, no ADB required.
I messed up on the signing and decrypting.
So for decrypting use the same method as encrypting.
As for Signing you will need an app on an other Android device if it works and get this app
https://play.google.com/store/apps/details?id=kellinwood.zipsigner2
After you got that you must move that decrypted file over to that device, open the app, select the input and output file, change the mode to platform and start signing.
After that was successful move the file to the file to the SD Card (if you have USB OTG support, if not then use PC) insert it into the tablet, go to recovery mode to flash it and you should get output, if you get errors in the output tell me them, if you don't remember them then try again.
Because we are on R5A's recovery it is really tricky to get that working.
It it fails then Sony must of either placed a special signing or a file still needs modifying.
Sent from my Nexus 4 using xda app-developers app