I've had these files sitting on my desktop for a while, and I've finally gone through them. These replace the uDWM.dll with one that makes the caption text left aligned.
8.0 left aligned caption text.7z includes two uDWM.dlls. I'm not sure what the difference is as they seem functionally the same without Aero Glass. Maybe 1 or 2 works better with Aero Glass, but I didn't test.
8.1 left aligned caption text.7z includes three uDWM.dlls. 8.1 left stock is meant for 8.1 without Aero Glass. 8.1 left aero and 8.1 left aero w7 have different offsets meant for use with Aero Glass. These might work for your theme or be slightly off. If they're slightly off, you can compare the hex code and make a patch by changing the modified bits.
Screenshot from 8.0:
winver from 8.1 with Aero: