The best way to reach the bolt at the engien mount is to use a flex socket on a long extension (I use a 24 inch extension for this job).
Universal sockets look like this:
Theoretically, it is possible to remove teh line assembly without unbolting the engine mount, but after fighting with a few of these in our shop, we usually do end up loosening the left side engien mount and jacking up the engine slightly to provide clearance. According to GM though, this is not necessary.
If I remember correctly, the lines on most of these vehicles (things do change in the design from year to year) are not bolted to the engine mount, but are attached to the engine block forward of the left mount with a small metal clamp. If you follow the lines, you can easily see any clamps attaching them to the engine; there is nothing hidden that any of us are aware of.
As I mentioned, this is a rather difficult unpleasant job requiring working in tight uncomfortable positions. There really are no secrets; it is a pretty straightforward repair process. As I read through the answer I have provided, I do not see anything missing; all the information you need to complete this job is here. If you get stuck during the process, let me know and I can try to help.
Something you may want to consider is resealing the oil filter adapter that the lines connect to at the engine block. There is a small gasket and an O-ring in between the aluminum adapter and the block that usually start to leak around the same age as the lines do. The parts cost around $2 at any Gm dealer parts department (they are not available at any parts stores that I am aware of). If youa re taking the lines off, it only takes a couple extra minutes to reseal the adapter so that you dont have to go through this unpleasant process again later...