I am having exactly same problem. Could you please help us with that ? Thank you.
I gave this problem to our releller's support, they did not have an answer either. They said it was a limitation and would need to be addressed by Solidworks. I am sure someone has figured it out? Surely there are folks out there with charted drawings with lots of part on them?
For some reason the design table can only be 8.5 inches wide as formatted in Excel, based on the font size. To get more text into the drawing, you can make the font in Excel really tiny, to fit more text into 8.5". Then, after inserting it into the drawing, you can stretch it so the text size is right. You have to do the scaling by eye.
Yes, this workaround is ridiculous. The same goes for most everything about formatting a design table for a drawing. I write some of our CAD procedures for our division, and it is embarrassing to have to put such things in print.
Edited 3/26/14 for clarity.