Small caps plugin for GIMP
Years later and there still doesn't seem to be an easy way to do it, so I had to kludge together a solution.
Firstly, type out your text in ALL CAPS.
Secondly, select the last letters of each word and change the font size.
And you're done.
This is the quickest and easiest way to edit a small amount of text, taking only seconds to do. If you need to do it with a lot of text then I suggest finding a better solution.
Note: The edit box seems to be buggy and loses the selection, or won't resize. It is best to avoid using it if possible. This may just be my version of Gimp however. YMMV.
Gimp 2.8.10
The FreeType GIMP plugin has been officially discontinued, so the only way to type in small caps in the GIMP is to use a small caps font variant such as Delicious SmallCaps:
Sadly, there isn't any better solution at this time. While it appears that there was a preliminary version of a Script-Fu script for generating small caps posted in 2005, it is no longer available.