If editing is disabled, you cannot put an inplace editor. Alternatively, you can add a read-only inplace editor as well
procedure TForm1.TMSFNCDataGrid1GetInplaceEditorProperties(Sender: TObject;
ACell: TTMSFNCDataGridCellCoord; AInplaceEditor: TTMSFNCDataGridInplaceEditor;
AInplaceEditorType: TTMSFNCDataGridInplaceEditorType);
begin
if AInplaceEditor is TTMSFNCDataGridEdit then
(AInplaceEditor as TTMSFNCDataGridEdit).ReadOnly := True;
end;