There is an alternate way to tie the cave knot that is looser... Joel at TDL tied a boltsnap onto the SPG I bought from him that way, and I've copied it once or twice since. Although now that think about it, that would let the snap wander up and down the cable, since it's looser... Oh well, I guess we're back to "we'll see"!
I've also seen the cave line tied to the swivel connector of the SPG hose, rather than the neck of the gauge.
For the purposes of the low-pressure miflex though, I haven't yet seen a boltsnap tied to anything other than the rubber part of the hose on a primary regulator.