Hey Richard,
I looked at your previous post, and turns out that I actually have a similar need; I'm trying to figure out a way to control the functionality of the tagged file sink because I don't want it to create so many files lol (I'd just like it to place everything in one file).
So I was thinking, since we already have the source code for these blocks, and there's a nice tutorial on how to write blocks either in c++ or python at
http://gnuradio.org/redmine/projects/gnuradio/wiki/OutOfTreeModules, so a good starting point would be to create our own version of the block, and use the current source code as a starting point in adding the extra functionality that's needed.