Hello Jorge,
This is my observation.
I tried the approach that is suggested above as a very first thing, but it is through CPP file. So, it didn't work. Then went to the approach I mentioned in my query as per ARM reference manual. That also didn't work.
So the solution I found later is that, I implemented a C file with this ISR interface (just as you mentioned) and then provided function calls to register a callback function to call from C++ Classes.
Please do let me know if that doesn't make any sense.
Thanks,
Hari