opening a new instance of Excel

If I already have a XLSX file open, and from explorer I double click on
another XLSX file, it opens within the same instance of excel. I have to open
Excel and browse to the file and open it in order to have both deisplayed
side by side (I know you can display both in a single instace but its not as
easy to use if you need to see both at the same time. My question is this; is
there something that I can change so that when I double click on an Excel
file, it will always open in a new instance, instead of opening in the
instance that is already running?
Thanks for your reply