Redmine

We're using Redmine 2.1.3 in the company, and would like to use some plugins which are currently compatible with 2.0 only.
The developers are not currently able to devise time to maintain their plugins, so I'd like to try and fix it myself.
I'm not a Ruby developer, hovever, I've successfully monkey-patched some plugins earlier. So, I would be grateful if someone shows me the right direction - I'll do the rest myself.

Example problem is like this:

Started GET "/users/30/edit" for 192.168.44.1 at Пнд Окт 22 17:23:05 +0400 2012
Processing by UsersController#edit as HTML
Parameters: {"id"=>"30"}
Current user: admin (id=1)
Rendered users/_mail_notifications.html.erb (12.5ms)
Rendered users/_preferences.html.erb (412.0ms)
Rendered users/_form.html.erb (446.3ms)
Rendered users/_general.html.erb (453.8ms)
Rendered users/_groups.html.erb (10.5ms)
Rendered users/_memberships.html.erb (105.9ms)
Rendered common/_tabs.html.erb (583.8ms)
Rendered users/edit.html.erb within layouts/admin (599.7ms)
Missing template, responding with 404
Rendered common/error.html.erb within layouts/base (0.1ms)
Completed 404 Not Found in 646ms (Views: 13.6ms | ActiveRecord: 8.3ms

This one is seen on many plugins compatible with 2.0.x when run on 2.1.x.
What is the way to change it to be compatible with 2.1? Is there ay manual or a general idea?