Can you not borrow a portable or something like for the install. I would not install it without a tv to test it on as I would have no way of knowing if the box works, calls back, etc - too many possible problems.
The engineer can refuse to do the install without a TV being there. He needs to see a screen in order to do the callback, or he may not get paid for the job. A portable with a scart is a sensible idea.