You can RMB in the BOM & there is an option to split the BOM.
Hope this what you are after.
To elaborate on what Ian posted, you can highlight a row of the BOM and right-click. "Split above" and "Split below" will be two of the options in the drop-down.
As of SOLIDWORKS 2014, you also have Horizontal Auto Split, and in there, you can set the length of your BOM and whether you want to keep that length one time or continuiously.