Blog post- or page- wide option of a plugin?

Hello.

I’m using a plugin which has an option that is global. This is option is set on the plugin’s settings page. I want to modify this plugin so that this option would be set on every blog post or a page. Like a little widget with this option on a blog post or a page edit page.
Can someone point me to the right direction (wiki pages, etc)?

Thank you.
Grigory.

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