Hi:
I agree with you. For one thing, putting the header vertically, assumes that you are always going to have a "fully-sighted" person reading the report. It would be horrible for someone with limited vision using screen reading software to have to deal with a vertical header like this. Using vertical headers may save space on the page, but it is not really "user-friendly" or reading software friendly.
Just because something is "possible" doesn't mean it's a best practice. I find that a lot of "requirements" involve needlessly jumping through cosmetic hoops. Requirements like this for vertical headers should be re-examined. Granted, the requirement was to be able to generate the headers vertically or horizontally. Why bother with vertical headers at all?
However, the original question that ended the post was: "should i tell my boss this new requirement is not possible? " So, it's possible. But, I agree with Bill -- in my opinion, I don't think it's the best idea to implement for the reasons stated above.
cynthia