I thought I remembered seeing a hack somewhere which described a
way to add a 2nd split bar to a worksheet.

You can divide your spreadsheet into 4 scrollable regions, although each
section is not totally independently scrollable. To do a quad-split, do the
following...

1) At the top of the vertical scroll bar, there is a small rectangle (it
almost looks like a min-button)... click and drag it down to the middle area
of the grid. Your spreadsheet should now be in two scrollable sections.

2) At the right side of the horizontal scroll bar is a similar looking
rectangle... click and drag it to the middle of the grid. Your spreadsheet
will now have four scrollable regions.

Is that what you were referring to?

Rick