Perhaps it's not an abuse... I just Googled OpenEXR meta-data, and came across this interesting quote:
"One thing that has been really interesting in the last couple of years has been the OpenEXR format for carrying images – in addition to being a floating point, 16-bit capable format its also an instructionally related format which means that the header is a database about the original material in the picture file.
"If we had an image sequence of OpenEXR frames I could take the original image with the unfilled header information and ship it to you in another country and you can work for three weeks on that image and then instead of sending me back the picture and the header information you send me back the header information only which of course is vastly smaller than the 16-bit picture. I apply that to my original 16-bit picture and it recreates that set of instructions that it receives from the header and I end up with the same picture that you are seeing on your screen."
"The header is instructions and comments about the work done to the picture and the picture itself remains intact you just send me the instructions – here's what I did to modify this VFX shot etc..."
In any case, I'd just like to register my gratitude that TG2 does output in this wonderfully flexible format.