At the moment we have rws.bid() function which participates in an auction for a subscription, and if succeed, buys the subscription for the address which initiated the call

In real world usage we noticed it would be convenient to buy a subscription for another address.

For example, we have a device that sends datalogs to Robonomics and we need to have device's private key to initiate a subscription purchase from its account. If we have a number of devices, it leads to managing a lot of private keys. Also as a side effect, we will have XRT "dust" on a lot of accounts. Instead, we could have one "manager" account, that purchases subscriptions for every device with only public address known