It's possible to redirect sys.stdout and sys.stderr temporarily to files. See Example 10.9. Redirecting output from Mark Pilgrim's Dive into Python.
Note: Redirecting stdout will also send the Sage prompt sage: to the output file. You can suppress most of the prompt with sage.misc.interpreter.set_sage_prompt(''). I don't know if it's also possible to remove the colon that IPython inserts.
And also by the way, you might find IPython's "magic" %logstart and %logstop commands somewhat useful. See %logstart? for options.