Hello,
I am not sure if I understand correctly what you need, but...
There is a possibility to upload supplemental files to a publication. They can be accessed via an URL and are not visible in the table of contents. (There is a link to supplemental files in reading tools, if the reading tools are activated). They somehow belong/relate to the publication (according to their meaning, as the name suggests it, they supplement a publication). So, if this is what you need (because you said "that relate to a paper") ...
Else, another possibility, maybe, is to use the static pages plug-in (s.
http://lib-pkp.lib.sfu.ca/wiki/index.php/Ojs_plugins or
viewtopic.php?t=3437&f=28). I don't know if it can be used with 2.2.1 but it is definitely in 2.2.4.
Hope this helps somehow...
Regards