Hello Marthin,
Well difficult to say, never done it.
As you know, you cannot have both ODWEK 8.4 and 8.5 at the same time installed in your server... meaning that with a single web server, you won't be able to do what you want to achieve...
With an Application Server (JBoss, WebLogic, WebSphere), you can do something like that with a servlet (java).
But not with the cgi, simply because the cgi is only a shell for the static library.
For me the only way is really to use either ODWEK 8.4 or 8.5... just decide on one.
Personally I would say 8.5... (8.5.0.
.
Sincerely yours,
Alessandro