I have some progress with this and it's very interesting.
First off, I have been testing and I can confirm that ALL previous TG-16 WiiU VC's titles that has already been released on the eShop SUPPORTS TG-16 CD, only tested the ones that are currently available from you know where.
You can test this yourself by copying the "pce.pkg" file from Lords of Thunder and put it on ANY of the previous TG-16 VC's and the game will boot and play as per normal.
I have successfully been able to inject "Castlevania - Rondo of Blood" into Lords of Thunder, the game and audio works fine, however the OGG audio files is not working, so the intro has no sound.
I suspect it's the OGG file related and needs to be specific on how big N is encoding.
Here is what I found,
Wii version = 48,000 Hz at 64 kb/s
WiiU version = 32,000 Hz at 56 kb/s
So I'll give it another crack at this tomorrow.
Here is how you do it, please be advised, not for beginners, if you don't understand what I'm about to say, then it's not for you.
Read my previous reply and click on the link and have a look at the "Dumping and Modifying the ISO" section, in short you need to get the Track 2 in ISO format, compressed and renamed file to .BIN, this is all done in the tools provided in the link.
You need to open "pce.pkg" file from Lords of Thunder with hex editor, HxD is your go to app.
At OFFSET: 000000B0
This is the HCD info, if you follow the previous step, you will get the HCD file, this HCD file is kinda like the CUE file for ISO/BIN files, this contains all the info of where the OGG files should be and the data BIN file. Once this is all working, this info is very important, but for now, it's not relevant since we are just injecting the DATA/ROM info.
At OFFSET: 0002EFC0
This is where the BIN data is located, pretty much open the Track 2 BIN file in HxD, copy ALL and delete and replace the info here, make sure there is a "00" value BEFORE and AFTER you pasted the Track 2 BIN info.
Save the file and put it back and test, if done correctly the game should boot.
That is as far as I got, now we need to get the OGG files working, I have read that the HCD info is very important as the audio can get out of sync with what is showing on the screen, mainly games that require the OGG files.
It's late and I might probably left some very little info out, but I'm sure you can work it out.