We can use two cells to define the range, like:
select-grid-range [get-item "Item #4" | get-item-cell -column "First Column"] [get-item "Item #7" | get-item-cell -column "The Column #2"]
this code line will select eight cells.
don't forget to change documentation of select-grid-range
also, verify compatibility with ctrl+selection, QS-2936