Off the top of my head, the only way I can think to do this is by some tricky fiddling with unix ids (which you can get in system events processes suite). But please, why are you making this huge headache for yourself? Unlike Linux, the Mac OS is designed around singleton instances of apps. You can convince it to open multiple instances, yes, but it's not something you should normally do without an awfully good reason, and when you do it with a big, complicated, greedy app like Safari you waste huge amounts of system resources and force yourself to jump through endless hoops in order to trick the system into doing something it's simply not intended to do.
Now, in my experience anyone who asks a question like this is going to pursue it come **** or high water. The fact that you've gotten to the point of asking for help implies that you've already expended a lot of time and effort on the problem, which implies further that you are fixated on accomplishing the goal. I will say, pro forma, that you ought to stop trying to make your Mac behave like a different OS and get used to the way the Mac OS works; that would be the sensible approach. If you choose not to take that advice - and frankly, it would surprise me if you did take it - then I would ask you to please have the grace not to waste everyone else's time by asking them to tilt at your windmill. Pounding your own head on such a pointless exercise can be written off as eccentric, possibly even romantic in a strange sort of way. Pounding other people's heads on it is just rude.