If we assume it is like the GTV6 the official upper sump removal instructions will start with 'remove engine from vehicle'.
I can say that I did remove the upper half of the sump from our GTV6 without removing the engine. I can not say it was easier that way... Many of the bolts are difficult to access. I used various combinations of short wrenches, long wrenches, deep sockets & regular sockets, universal joint drives and a liberal apllication of Italian swears. I also had to remove the alternator & move the A/C compressor out of the way. The left side engine mount has to be removed to get to one bolt on that side (supporting the engine with a jack from underneath). Finally, the engine has to lifted up an inch or more to maneuver the upper sump past the crank & front crossmember. And I have a four post lift that makes working under the car much less unpleasant.
So, probably the easiest/best way is to remove the engine...
Can you share with us some pictures of the carnage? Also what was it like inside the car? Did it deflect the path of the vehicle. Also did the entire car travel over the bump? Anything else get pulled off, like the exhaust?