Is this a terrible idea? Is it dangerous? No idea. It seems to work just fine for me, and darn, it sure is faster. I would be curious to see what others have to say.
After you have successfully set up sendmail, edit /System -> Library -> StartupItems/ -> Sendmail -> Sendmail, and find these two lines:
/usr/sbin/sendmail -bd -q1hEnclose them in parentheses, and put an ampersand immediately after:
/usr/sbin/sendmail -C /etc/mail/submit.cf -q1h
(Restart and (hopefully) enjoy.
/usr/sbin/sendmail -bd -q1h
/usr/sbin/sendmail -C /etc/mail/submit.cf -q1h
) &

