Shield Other was just off the top of my head. It's already producing flamethrowers and ice missiles, so visualizing can be "it's just magic."
If you don't want to go that route (understandable) there are still other ways. I'm thinking perhaps an armor upgrade that allows one to incorporate a shield into one's armor or something that starts one down the 'protector' line--a tower shield without the attack penalties would be badass, just off the top of my head. Perhaps include a way to take attacks in place of adjacent allies. Higher level abilities could be something like counting the Templar as a wall that blocks line of sight/effect, making it so allies can literally use him as mobile cover (the Templar is still target-able as normal, of course). Maybe if he has the protector upgrades as well as some of the mobility upgrades, he can take an immediate action to move X squares and push allies out of the range of an attack to take the blow instead.