2 psu's??

Ok,I just bought the new Gigabyte X58A-UD9 and the Lian-Li PC P80 Armorsuit.I have some components left over from a previous buid.I want to take full advantage of the 4-way sli,but considering all the components I have in my rig,I dont think my current Psu is sufficient enough to handle 4,3,yes,but 4,no.I have a Silverstone 1000w Psu collecting dust until I can build my younger brother his X-mas gift(awesome gaming rig).My question is I have plenty of room in my case to mount this extra psu,but can I use it to help power up a 4th gtx-480?And if so,how would I go about doing it without destroying over $6,000 worth of precious equipment.The reason I asked is because I see suggestions on line telling people to use a second psu.I know the performance gains will be little but I wanted to utilize all the stuff I have.My build i have is on my profile.The only things I changed were the mobo&case.