Using User Profile fields in subscription mail templates

Hi.

I've managed to write a module that implements hook_subscriptions_add_mailvars(), hook_form_alter() and _mail_edit_variables() so that I can use author and recipient profile fields (from Profile module) in subscription emails. So far, this works well for the email that gets sent out when a node (forum in my case) is created.

However, it appears that $mailvars['!comments'] in subscriptions_content.module cannot be similarly extended, as it is fixed in _subscriptions_content_format_comments(). I don't want to modify the module, so I'm hoping someone might be able to tell me where to find a function that in the subscriptions or mail_edit modules I can hook into in order to add elements to the $mailvars['!comments'] array.

Thanks!
Muyi