Implement a role queuing system and have a separate ELO for the support role.
The biggest issue when trying to come up with a new ELO system is trying to figure out how to determine a players skill level when it comes to support. By having a seperate ELO for support you solve the biggest issue with the current ELO system determining a players skill level by K/D ratio and Gold earned.

Queue as support ELO based off win ratio.
Queue as another role ELO based off win ratio, K/D ratio and Gold Earned.