Hi,
there doesn't seem to be any simple way of sub-contracting to others. Unless the person supplies their own van and equipment etc its easy to fall foul of employment law. Something I discovered recently is that if the worker is already registered as self-employed for themselves, you can pay them up to £112 pw without having to register as an employer and they can use your setup.
Obviously there's many more aspects to this discussion but I thought I'd put my contribution in as a starter.