The original H18 equipment included a short length of 1/8 line for jib luff tensioning. This tied to the tack shackle. You hoist the jib and before zipping closed the last few feet, hold the halyard, Pull the 1/8 line from the tack shackle up to the halyard wire thimble or block (if there - older models) and back down to the luff cleat. Untie the longer line and stow in the tramp pocket. Once the rig is tight, main up... sheet the main to fully tension the forestay. Adjust the jib luff tension with the short line and luff cleat (very little load on this is required to remove luff wrinkles). Half hitch the line around itself to lock into the cleat (keeps the luff tension from slipping) and zip the luff closed, tucking any excess line inside.
http://www.hobiecat.com/support/pdfs/H18&SX_Manual.pdfManual Page 9, Fig 16 shows the halyard setup before stepping the mast.
Page 16 shows the steps above. Images too.