Order Confirmation Mail Customization (adding Global Attribute)

[ansem]

I want to add one new field to the order confirmation email, integrating with one of the newly created Global Attribute.
Say, I have created a new hidden Global Attribute called "donor", and in the order confirmation email, I want to display this attribute between "Product" and "Model" field.
How do I do that? Could you please show me where the related codes are located? Or is there any existing extension that could achieve this?

Thanks in advance.