[JohnRPollard]

Faster's advice is sound on this. Much better to get the lead for the tack line forward of the headstay.

[Here I'm assuming that by gennaker you are referring to a sail that is akin to an asymmetric cruising spinnaker. If you are actually referring to a gennaker with a taut line or wire in the luff, or one that is on a furler, then the advice below does not apply.]

Folks that are using a padeye on the foredeck (aft of the headstay), as an attachment point for a block through which they run their tack line, are usually doing so because the padeye was there in the first place as an attachment point for a conventional spinnaker pole downhaul. If you don't have the padeye, and don't plan to fly a conventional (symmetric) spinnaker, you don't need the padeye.

Also, the piece of equipment that you refer to as a parrel is not usually necessary if you have a true asymmetric spinnaker/gennaker. Sometimes it's helpful to have one, but they are more often used when someone is trying to fly a symmetric spinnaker like an asym -- i.e. without a pole.