Speaking as someone who writes embedded software using USB stacks for a living, there are a number of solutions to this. Your solution is possible, and is how

Speaking as someone who writes embedded software using USB stacks for a living, there are a number of solutions to this. Your solution is possible, and is how many iPhone USB charging cables are designed. If limited communication is required, the device being charged can also contain a separate processor for the interface. The ideal solution is for the device to contain some security measures, to prevent these issues; this solution is also the least versatile or most costly depending on implementation, and may not be achievable.