Extend the Bulwark (Combat, Teamwork)Source Magical Marketplace pg. 6 (Amazon)
You can bolster a trained ally’s defenses by interposing your own armored body.
Benefit: If you are wearing medium or heavy armor and are adjacent to an ally who also has this feat, as a free action, you may give your ally a circumstance bonus to her AC equal to half the armor bonus provided by your armor. This bonus lasts for 1 round. During this round, you gain no bonus to your AC from your armor.Source Armor Master's Handbook pg. 20 (Amazon)
You can spend 5 stamina points either to use this feat without losing your own armor bonus to AC, or to use this feat to grant the bonus to an ally. (Magical Marketplace 6)