I'd tie the line down, run it through the cringle at the "reef tack" and then down to the other side of the boom. You get a 2-1 purchase, you can tighten it by hand, etc. If you want, you can tied it the boom.

We used to use this set-up when we led a line back to the winch under the dodger. We have places to attach lines and block at the base of the mast.

Also, when you go from port to starboard, you keep it in approximately the same place with a little "shifting"

Be careful that you don't compress the sail and affect the full battens or cars. I've winched my main tight and screwed-up Antal batten cars. If you can bring the tack down without causing "problems" with the sail fitting below, mark or use tape for the places you want on the halyard and reef tack line tightened to.