I had the same problem as you and eventually found an easy way round it. I wrote this to be added to the instructions but it was rejected: "Once the DVD drive has been removed, remove the 4 rubber washers from the screws removed earlier and insert them into your new DVD drive. Because two of the screws are difficult to reach, it is best to insert these two screws into the washers and then slide them into place ready for securing to the base plate".

The rubber washer holds the two screws roughly in position, you can then reach them with your screwdriver through the two holes (about an inch away) and finish tightening them up.