As long as you retain the cats and the O2 sensors, you can cut out the factory "Y" pipe and fab up a 'true dual' setup... You'd want to incorporate an "H" or "X" pipe between the new dual pipes and not use too large a dia piping.. Something like 2.25".
But, it won't really gain you all that much, except for maybe the sound... If it was me, and you still want the dual tailpipes, go for the single in/dual out muffler as mentioned above and you will save yourself a lot of headaches in the future... ;)
Good luck!
Mitch