FWIW: you could implement something very much like what you want, using gcc or llvm on *nix. Not sure about windows - never looked into it.
In particular: you can step through your instrumented executable in your debugger - and explicitly dump coverage data via the relevant callback.
However: the performance you see (from coverage callback to display update) may be poor for various reasons which may or may not be easy to address.
A bigger issue is that this seems like a pretty unusual use model - so it is unlikely that a vendor would implement it.
I confess to be not understand what you are trying to do/what questions you want to answer such that your proposal is the best approach.