One cheap and easy way to do this is to drill a small (50 to 100 mils) hole in the center of the pad on the PCB. Solder the pad itself but not so much it puddles. Solder or at least flux the pad on the IC and solder just the corner pins to the PCB. 

Put a 60 watt or so solder iron with a *small* chisel tip into the back of the PCB and into the hole you drilled. This will heat the IC pad and the PCB pad enough to fuse together. Use a gloved finger to press the IC flat as it fuses to the pad. STOP the instant this takes place. Now you can manually solder or use infra-red or a heat gun to solder the remaining pins.

This works well once you have done it a few times. You do loose some heat transfer to the PCB using this trick, but less chance of damage from cooking the IC or PCB if other procedures last too long.

EDIT: The only time this trick will not work is with multi-layer boards and you know there are traces you might cut through. However IC's that have a bottom pad for grounding and/or heat sink normally have no hidden traces under them. At most there would be a grounding pad with a ring of SMD capacitors around its perimeter. Unless it is very small it is still safe to drill a small hole in the center.

Thanks to @MichaelKaras for his suggestion that if you are doing your own board layout, a 50 mil hole can be embedded in the board that is plated through at the board house. This creates more surface to transfer heat and avoid drilling burrs in the copper if it is done later on. The plate through also allows more heat to be picked up from the solder iron so this step happens fast. Also it allows you to route a few traces around the hole if it simplifies routing.