You could try using an actual tapered fly leader tied into your main line with the torpedo close to where it is tied on. Try to slow or stop your cast to get the fly to turn over(flip past the float). Would go with a 7.5 foot leader. Can join leader with back to back uni or nail knot.
And as Red Bullets suggested add a good swivel might be a good way to join the two together(and help combat line twist) then slide the float right up to the swivel (but not tight against it).
Could also add a small indicator on the line to help, but not sure how it will work together.
Hope that helps.