I race with an Asymmetric Spinnaker, and have installed a Selden retractable bow sprit. Prior to that, I simply shackled a block to to stem head fitting in front of the forestay attachement, and ran a tack line aft from there. The parrel beads (or ATN's "TACKER") or other such devices help to keep the tack of the spinnaker from spilling off to leeward - which can be a problem when trying to use the spinnaker when the apparent wind angle move forward. Any time the apparent wind angle is aft of the beam, I have found that they aren't needed, but YMMV.