I am now seeking to answer this question.
It seems a counterproductive workaround to import the entire file into a string and then write a script to parse its contents. Or to put it another way, I expect MathWorks to have a more eloquent solution already prepared that I merely need to find.
One workaround is for Velocity: Instead of creating the "full" multiple-tissue DVH one wishes to export, one must save to multiple files a separate DVH for each organ of interest, so that there is only one data set per CSV. This is not ideal, but it seems faster than continuing to search for additional ideas.
Edit: Walter, I thought it was not uncommon for data to be written sequentially (i.e. appended end-to-end); old magnetic tape comes to mind. Because I thought MathWorks had prepared for common data files, I thought there was a command or option I was simply unaware of. I am sorry if this expectation was incorrect, but I don't see why it was unrealistic. I have attached a sample data file to the original post.