As far as I know, there is no way, and if the text is really long, the font may be too small to be readable.
Crystal does not provide any means of determining at run time how many pages it is going to use.
What you might try is building test cases. Crystal does have the len() function and depending on the length of the text, you could change the font. This would be a lot of trial and error, I think, but it is the one approach that might work.
HTH