I think if the source files are still changing, then staying with attach seems like a good idea. Once the source is stable, you can import everything using python's import -- to get this to work you just need a blank file __init__.py, and a file all.py listing what to import (maybe you don't need every function from every file). Taking a look at subdirectories of the Sage development directory will make this obvious. And you can also take a look at the python modules reference if you want, although it doesn't quite agree with what Sage seems to be doing.
import glob