I quite agree, there's certainly been talk of those two institutions -- as you say, they are not pension funds or private individuals. The talk seems to get stronger today, as an article in the Austrian paper Kurier claims to have leaks on a plan steered by Merkel and Sarkozy to be able to back Greece with €55bn, €20bn from Germany, half guarantee, half KfW, and €10bn from France, with other EZ countries that are able making up the rest.

Also see this from a couple of weeks ago, where it's suggested that Euro system central banks hold the major part of Greek bonds.