Jude,
While I understand everything that you are saying, I still don't see where tying up the 7-8 will do you any favors. If you're playing me, I just pass it back to you, or I'll jam you up.
The safety I illustrated is not very difficult if you can control the cue ball speed. A version of this same shot is in my book, Lessons In 9 Ball, in a section dedicated to safety play.
I don't think being spotted anything really has any effect on this situation. If I get on the 2 ball, I can break that 7 and 8 up very easily. So much for tying them up.
In my shot, admittedly I just looked at it for about a millisecond and made a decision on the shot I illustrated, but I looked at what the shot did or didn't do.
#1 - I can hide the cue ball behind 3 balls. If I get close enough to the 3 ball, I take the jump out of the equation.
#2 - If I hit it too soft, he's still banging the 1 ball into the rail, or playing safe back on me.
The one does not need to go as far as I diagrammed it to make this a nightmare for the opponent.
The last thing I would do is tie something up here, because all the guy has to do is pass the shot back to me. Then what do I do? Seems redundant to me to do that, getting the 6 or not.