After receiving some threats of the copyrights holder of a dual licensed software(GPL2 and commercial) to buy the commercial version for projects in production, I am thinking to make a fork.

In a case of GPL2 and commercially dual licensed with business owned copyrights software, is forking the GPL2 version an option?

Also, is forking a good way to deal with such cases?

Background information

The software is a web CMS released under 2 versions a GPL2 free open source edition and a commercial edition including technical support and extra functionality.

The problem is that now, basing their argumentation on the "distribution" definition of the GPL2, the company holding the copyrights argue that delivering the software and some extensions to a client is considered as a "distribution". And that such a "distribution" falls under the GPL2 obligation to release the custom made extension code.

Custom made extensions are mainly designs, templates and very specific functionality.

Basically they give me 3 choices:

1. Buying the commercial licensed edition for projects based on the GPL in production,
2. Deleting all the projects in production based on GPL2 version,
3. Releasing all the extensions as GPL2 code.

The first 2 options are nothing realistic for finished projects.

The third option could be fine, but as most of the extensions are very specific, cleaning the code to make it usable by other users means lot of works and also I am not sure the clients will appreciate to have their website designs and specific functionality released publicly.

The copyrights holding company even contacted some clients directly, giving them the "choice".

I know that this is a very corporate interpretation of GPL2, and a such action is nothing close to legal, but as an independent developer, I don't want to take the risk to get involved in some long and tiring legal procedures.

PS. This question was first asked on Stack Overflow where it felt out of the scope and closed, after reading the present site FAQ, discussing about software licensing seems fine.