The shape do look similar but the lines are totally different. So no, it will not be easy. The grill of the ES300 is even part of the hood. The time and money spent trying to install ES300 headlights onto a camry is too great IMO. You would have to cut into the fender, hood, bumper, radiator support, and wiring. Might as well just install some clear corner lens.
There are a few members here that have install the more updated Gen 4.5 headlights on to their gen 4 that required a bit of trimming and cutting of the radiator support. Some even went ahead and change out the bumper and grill.