Heimer passive concept
P: Techmaturgical Repair Bots Heimerdinger has a swarm of repair bots swarming around him, causing nearby allies to regenerate a % of their missing health each second. Champions: 3% per second if champion/turret damage hasn't been taken for 5 seconds. Structures: 5% per second Evolution Turrets: 100% over 3 seconds if non minion damage hasn't been taken for 5 seconds.
If a strategy of "sit at a tower and heal it for 30 seconds" arises, so be it. If anyone should be able to do that kind of thing, our resident mechanic should be the one.