Basically, it can't be done with RM's current modal window design. Non-modal windows have been on the RM wish list for a very long time. Only the RM developers know if non-modal windows will be included in the RM rewrite that is in progress.
The closest you might be able to come would be to have two completely different but identical copies of your RM database open at the same time on two different machines, or to have two completely different but identical copies of your RM database open at the same time on the same machine - one copy open with the regular RM and the other copy open with RM-to-Go. But this only gets you to two windows, and I think it also is likely to lead to disastrous results if your two "identical" copes of the database get out of sync, which they almost certainly will. Plus, it could be very confusing which of the two copies of the database that you were working on at any instant in time.
I'm a strong advocate for non-modal windows, and in general I think software that supports non-modal windows is much easier to use and much more user friendly than software that supports only modal windows. My only caution is that if developers are not very careful, non-modal windows can be implemented in such a way that the software is very confusing (especially for new users or users who are not especially fluent in using computers), so that it's quite possible for non-modal windows actually to make things worse. So I want RM to support non-modal windows, and for RM only to support non-modal windows in a way that makes things better, not worse.
There are a few things you can do right now that can help a little bit. One is that it's possible to run RM's help facility in a totally separate window from RM itself. You do so by making a shortcut for C:\Program Files (x86)\RootsMagic 7\RootsMagic.chm. (I'm assuming the default RM installation. You would have to adjust this shortcut if you don't use the default RM installation.) Another is that you can view media in a totally separate window (and probably with a better viewer than the one built into RM) by loading your media files into RM as a File rather than as Media. That can be a mixed blessing because files loaded into RM as a File cannot be printed from within RM. Also, it's apparent from comments on this forum that many users prefer media files to open within RM rather than in a separate window despite the modal window problem. The last thing I can think of right now is that if you use RM's WebSearch View, there is an option to Use external browser which results in a totally separate window for the search rather than a modal window within RM itself. Again, comments on these forums suggest that a lot of users prefer not to use the Use External Browser option so that the data will appear in a modal RM window.