How to use two databases within one model

For an online shop I will have to work with a legacy data base for
some of the models.
Furthermore, within my application those models will need additional
attributes that I will have to save in my own database.
I was thinking of using aggregation, encapsulating the legacy data in
their own ActiveRecords::Base objects, which I would configure to use
the legacy database. Then I would wrap those objects into other
ActiveRecords::Base objects that would contain the extra attributes
and use my own database.
Do you think this is a viable approach?
In the docs I read that composed_of is meant for value objects not
business objects...
Has anybody solved a similar situation?

Chances are I won't even be able to access the legacy database
directly, but will have to query it through WebServices.
Does anybody have a suggestion how to go about if that were case?

Any feedback is highly appreciated!

I’d be interested in anything you or any one else has found out on this. Any one have any ideas?