Agree with everything that has been said.
Ben, if you want to go down this path you'll need to find some 400lb+ hollowcore to splice onto your mainline. Something like JB or TufLine XP would be a good choice.
Splice this for a 2/3 metres, leaving enough room to then splice on your mono shock leader (i'd be thinking around 50cm or so).
It's been a long time since I've done this, and I did it with the cats-paw/twisted connection as mentioned. You would need to experiment with the single though as I haven't done it and that's merely an observation. Many French anglers use this system (i.e. Eric Le Guyader) and they may weigh in on this discussion.