To add the social login icons anywhere, you can use the following easy-tag:
That will show all the social network login buttons using the icon.png files for each provider from the /media/sourcecoast/images/providers directory.
With that said, I don't know specifically where that should be added in the socialize template. You may want to contact the JomSocial team to get more information about what file to edit to alter that header area. Once you get that, just add the tag wherever you want it to display.