A neat trick when using this feature: When configuring the *.wdi file, the dialog boxes within AutoCAD 2008 limit the max column number to 60. This limits the amount of information you can specify for each of the nine device columns. However the *.wdi file is really just an ascii text file. In fact it is a series of AutoLisp commands setting AutoLisp variables.
Edit these files using a text editor, and the 60 column limit disappears. I have used 88 columns with no problems. Perhaps the developers can modify the dialog boxes?