Assign todo to the creator, voter or proxy-voter of an idea

The ideas portal is only available within our organization and we have a client facing team who raises ideas on behalf of the clients they interact with.

We have faced a few issues where an idea was set to 'Will not implement' but this failed to be relayed back to the client.

I would like to be able to set up an automation that triggers when an idea is set to 'Will not implement' and to create a todo that gets assigned to anyone who has voted or entered a proxy vote for the idea. However, within the automation set up screen, only the assigned user is available for assignment.