SQLAlchemy: add a relationship using id instead of object?

Is it possible to add to a SQLAlchemy relationship using ids rather than objects?

For example, consider two declarative SQLAlchemy classes, Review and Artist, with a relationship between them:

class Review(Base):
    artist_id = Column(Integer, ForeignKey('artist.id'))
    artist = relationship(Artist, backref=backref('reviews', order_by=id))
    # etc.

class Artist(Base):
    # etc.

With a list of review ids to add to an artist, I seem to need to look up the artist from the id, then add the artist object to the review, like this:

for review_id in review_ids:
    review = session.query(Review).filter(Review.id==review_id).first()
    artist.reviews.append(review)

I'm sure it would be more efficient to skip the lookup and just add the ids, but is this possible?