There's no way to make that field pastable in the datasheet view that I know of, but there is a workaround: create a new multi-line text field that does NOT have the "
Append Changes to Existing Text" option set. (this is the option that gives you the "view entries", as it's storing each change). Then, create a workflow using SharePoint designer. Configure the workflow to run each time an item in the list is changed, and have the workflow update the current item to set the notes field to be whatever is in the newly created field.
Then, create a view that has your new field, but perhaps without the original notes field. You can then paste whatever content in the new field, while in datasheet view, and the workflow will take care of copying the value into the Notes field.