Multicell select in edit mode with TStringGrid (or TAdvStringGrid)

How can I set things up so that multiple cells can be selected while
still in edit mode?  Alternatively, is there a clever way to toggle in
and out of edit mode contingent upon the user attempting to select
multiple cells?  I am using a TAdvStringGrid so ideas in terms of either
this component or its ancestor (TStringGrid) would be fine.