Basiclly like the title says Is there a plugin to help with this or do I need to edit the theme ?.
Theme hardcoded will surely work. (But any change does need external (by ftp or editor) theme change
Dependant on the theme you are using, the option to use a menu area (or create a menu area) so you have more possibilities? (like dividing by columns (blocks) etc.. (most versatile solution))
Inside using links which can be altered 'on site . (remember the v1 Core theme? that used links+img to parts of e107 in box form ( 3 in a row)
Best option (easiest; build on Jimako's reference) :
when in sitelinks create a Container link (eg main link for 'block' called Third Parties etc..) now create sublinks for those sites you which to link too.
For ALL links (for this) use template x-footer (dropdown option whilst creating).. that's it. See site or menu manager where it will display (around footer)
You don't need a plugin depending on the theme, you can add links/html to the Settings> Preferences> Site Information > "Site Disclaimer" textarea, just be sure that admins can post html (I noticed on a fresh install that you have to set that in "Security and Protection" then delete the cache before it would allow the code to save properly and display properly).