The larger Asus G series have been a bit annoying to disassemble for a while now. If you remove the plate behind the screen the only thing you're going to see is going to be the battery, probably. To get to the fans you have to fully remove the keyboard top plate, which is almost a full disassembly. You also probably want to do a full disassembly if you've had it for a year and give everything, not just the heat pipes, a good dusting. My G752, even with the "dust release technology" had a few dust bunnies running around inside of it after about 10 months, the first time I fully disassembled it for cleaning. There are a few guides on how to do a tear down of the G751 on youtube and whatnot if you don't want to go in blind for it.
As for the idea for drilling holes, as was mentioned, the air flow was designed with specific channels of air in mind for a controlled cooling path of air. Adding further ventilation points may make your cooling system less effective as a whole. Before you resort to that I would recommend trying either software solutions to reduce heat, such as undervolting or using a program to increase fan speed, or a hardware solution like a cooling mat below the laptop to try and reduce heat by increasing airflow over the bottom of the laptop.
