Wait, using an external monitor uses the GPU more heavily? I have a 13" early 2011 MBP and for the first time ever I bought a thunderbolt to HDMI adapter yesterday to use on my little TV. I'm using it now. I don't/won't use this 24/7, but when I have time to relax, I'll likely be taking the laptop upstairs to use this bigger monitor.
I thought you knew the issue was for 15'' MBP. NOT YOUR 13'' MBP. Why are you so worried about using the GPU?