The user submitted a project, of which he is not the solely copyright
owner (since it seems he took it over). The license headers
unfortunately do not include the wording "or (at your option" any later
version". Can the submitter just add this wording?
Not without something to back it up. If the original copyright holders
indicated somewhere it's "released under the GPL", or there were
informal understandings that any version was ok, then it's plausible.
On the other hand, if all the known information from the original
copyright holders is "this is released under GPLv2, and only v2", then
there is no basis on which to change that. It would be necessary to go
back and ask them. (Or rewrite all their work, which hardly seems
feasible in this case.)