I think you're may wish to consider keeping the lazy jacks turning blocks toward the outer ends spreaders, further away from the sail. Then you can leave them in place while sailing, without sail chafe. No-fuss lazy jacks.

If you need to have lazy jack lines further aft on the boom, then make them multipart: Hang turning blocks from the lazy jacks about mid-way to the boom, and run a line on each side of the boom from the forward end of the boom up through the turning block on each side, and down to the aft end of the boom.

In the image below you can see my hanging lazyjack turning blocks -- I have a set of lazyjacks to each spreader (upper and lower) and leave them in place all the time without any chafe.