Hi julvr,
there could be two possible implementation in my eyes. One would be to use the shell extension plugin. Currently this plug-in only accepts parameters of a file explorer (see section File Explorer and Shell Extension Plugin in
http://www.codeblocks.org/en-docs-wrapper). Perhaps it could be extended to accept input from a editor selection. For example you could define a shell extension Firefox that executes a command like "firefox $selection" and opens the selection (e.g. url) in a browser. So you could add abitrary commands for you needs.
The next solution could be a modification of the codesnippets plugin. Currently you can add file links or urls (see section Codesnippets in
http://www.codeblocks.org/en-docs-wrapper) and open them via the context menu in the codesnippets browser. Perhaps it could be extended and provide a context menu even in the editor and to pass the selection as file link/url.
Just try to ask dmoore (Shell extension plugin) or Pecan (codesnippets plugin).
Bye,
Mario