You could create a string parameter and prompt the user to enter the text message. Then add a text box to your page footer (or report footer) and enlarge it to accommodate the message and make sure "Can Grow" is checked in "format text." Then drag the parameter from the field explorer into the text box.
This allows the user's message (limited to 254 characters in CR versions less than 9.0, I think) to appear on the report. The potential limitation is that the user will be prompted to enter their statement before the report runs. So you must be able to incorporate your statement in the parameter prompt field or they won't be able to read it before creating their own text message.
Although I'm not sure, maybe there is a way to have the parameter prompt/text box incorporated into an on-demand subreport, so that the user could first read your statement in the body of the main report and then prompt the subreport to run which would then prompt them for input. But I'm not a subreport export--maybe someone else could weigh in on whether something like that would work.
-LB