Hi Doug,
Currently the way report sections are rendered there is no easy way to flawlessly extend the vertical lines of a table.
The workaround to accomplish this is to draw the lines yourself. Through the designer you can add lines (Add Line button) and set their position exactly on the vertical lines from your table headers in the PageHeader section of the report. In the OnFormat/OnPrint event for the PageHeader you set the height of the lines to a certain length. The drawback to this workaround is you have to determine the height of the lines.
I've attached a report definition that shows how this is done. Through the VBScript you can obtain values such as Page number ("Page") and any section height. So you can make the lines a different height for page 1 (it may have a Report Header) and a different height for other pages without headers, report footers, etc.
Regards,
Greg L