I believe I found the proper way to do it. Here is the code to to put in the "tg_launch.py":
if __name__ == '__main__':
from gearbox.main import GearBox
gearbox = GearBox()
gearbox.run(["serve", "--config=development.ini"])
If you want to debug your setup (bootstrap code) use the following:
gearbox.run(["setup-app", "--config=development.ini"])
Refer to http://turbogears.readthedocs.org/en/latest/turbogears/gearbox.html for all available commands and options.