Creating companion magic item that grants feat to hero

[Vigoroso]

Hello. I am trying to create a magic item for an animal companion that does the following...

This ornate military saddle, tooled with an elaborate equine motif, grants the mount’s rider a +5 competence bonus on Ride checks and the benefit of the Mounted Combat feat. If the rider already has the Mounted Combat feat, she instead gains the benefits of Ride-by Attack feat. In addition, the mount gains a +5 competence bonus on Acrobatics checks and the benefits of any teamwork feats possessed by its rider.

My problem is two-fold.

First, how do I grant the feats to the hero (rider), and not to the animal companion to which the magic item is equipped. "...grants the mount's rider...the benefit of the Mounted Combat feat"

Second, how do I write an eval script for "If the rider already has the Mounted Combat feat, she instead gains the benefits of Ride-by Attack feat."