Aggregating multiple ActiveRecord relationships

The following pastie will help with my question below: help:
http://pastie.org/219582

A user has_many Items via both the User model as well as the user's
parent Account model . Other users are able to make their own Items
visible to other users via the AccountsItemsPermission relationship.

I would like to create a "meta" relationship for the user that
aggregates both has_many relationships at the User and Account level
into one, so there is an easy-to-access 'visible_items' relationship
that retrieves all accessible Items for a give user.

As you can see, I am currently using custom finder_sql to achieve this
goal, but would like to see if there are more elegant solutions to
this problem that wouldn't have to resort to finder_sql. One of the
disadvantages of finder_sql is that it is incompatible with plugins
like will_paginate.

Any ideas would be appreciated, thanks!

Jack