ANSWER:

I was thinking on developing this as I myself use GIMP & had this problem. I used the same workaround as Shawn pointed but when I started my research on developing a new Text tool, I found that GIMP 2.8 already had this functionality from this video (I’m still using GIMP 2.6 though). You might want to upgrade GIMP then you would be able to do a lot more than just bold a particular text with the new text tool.

Ravi Ojha from http://askubuntu.com/questions/310032