Michael, you can get there by different routes but the easiest is probably this:
In Graph Ordination menu, select File | Save scores as | Cols, then select spreadsheet.
In Excel delete rows (species) from this spreadsheet as desired.
PC-ORD, File | Import (as either main or 2nd matrix)
Tools | Matrix to gph
Close that matrix.
Then open that *.gph as the graph col file. (File | Open | Graph col)
Note that you might need to delete the corresponding columns from your main matrix, lest PC-ORD complain that your graph file doesn't match your main matrix.
Bruce McCune