Yes You can. Don't worry to much about heat. Biggest disadvantage I can see is space needed. Servers normally use 2 psu'so that if one fails server still continues to operate. Antec P190 case have 2 psuš from the factory. Or You can buy sparate psu specially for vid card, many of theese fit in cd bay.If You put two together Yourself it is good idea to separate them so that one feeds some componets and other different ones. For them to start up together You need to connect green wires together and any of black wires. Leave the rest separate. Anyway it is best just to get a more powerfull psu unless You already have 2 and don't have money for a new.
I know its not a perfect solution, but I spent a lot on upgrading my hardware this month and cant really justify buying a better PSU till next month. I was looking for a temp solution in case my PSU is not up to the job.
Thanks for your advice, it looks like I will be able to play Far Cry 2 this month afterall