Different power costs for individual miners within one client

We often run deals for customers where we offer discounted power rates if they buy more miners and continue to expand their fleet with us, or if they have older miners we sometimes do a profit sharing power rate with them. Currently, we have to create multiple client accounts for the same client if we want to have their miners reflect this “special deal power rate”. This means when we send them their power bill, we have to manually add up each of their client accounts' power bill. Instead, I'd like to be able to assign an individual miner within a client's account a power rate that differs from the client's “default” power rate. This way I wouldn't need multiple client accounts for the same client if the power rate differs between their miners.