Excuse me for jumping in on this, but this is something that comes in handy for me also. Just tried it out, and makes better sense then copying the file then opening both.
Just a few words of caution that sombody may encounter.
1. You loose your "Freeze Pane" setting. (no biggy)
2. If you have "Zero Values" unchecked (under Tools ~ Options) because you don't want to see all the cells that have formulas in them show zeros, this feature will default to "checked" in the new window.
So for item 2 above, be careful not to close window 1 and save window 2.
Just encountered those two problems myself.
h.h.