I found a solution (cheesy as it might be).
I found that the following file creates the smb.conf file upon boot:
/usr/pluto/bin/Network_Setup.sh
I created a file called smb.mythtv which contains the code I want to put into smb.conf.
Inside Network_Setup.sh I put in this line right before the service is started:
cat /etc/samba/smb.mythtv >> /etc/samba/smb.conf
Not eloquent but it works. If anyone have a more eloquent solution I'm all ears but in the meantime I'm up and running
Thanks for the suggestions!