The way to do that is by editing /etc/rc.local and putting the following in it:
su lindqvist -c 'autossh -N -f -M 29001 -R 19996:localhost:22 firstname.lastname@example.org' &
Make sure you put it before the line that says
linqdvist is the user at on my work computer I want to be running the autossh, 19996 is the port I'll connect to on my home router to gain access to the ssh port on my work computer. Since I'm using WRT54G with Tomato the remoteuser is root, and I got my dns (remote hostname) as shown in this post: http://verahill.blogspot.com.au/2012/02/tomato-router-and-free-dns.html
It's that simple.