Today I wrote a small application which will allow you to set some of the approval workflow settings on a per-site base. This apps will modifiy the workflow association for you on every "Pages" library in the selected sites.
You have the possibility to enable or disable the approval workflow, choose the participants of the workflow and allow or disallow to change the participants lists on workflow start.
I created this application to configure the approval workflow on a customer site. If you want you can download and extend the source code. You will see, that the association data is stored in a XML and with a little debugging you will be able to also modify the other parameters.
Here you can download the application including source code and Visual Studio 2008 project.
Update 10/17/2008: I moved the code to an ASPX, packed as WSP and uploaded to CodePlex. You can find the download on the MOSSApprovalConfig project site.