A simple modification to the boom is adding about four padeyes, in a vertical position, to each side of the boom. You can then do two things.
First, the lazy jacks can terminate at the padeyes...which gives you a nice four-leg lazy jack system that makes containing the mainsail pretty easy.
Second, you can run a shock cord (bungee cord) through the padeyes on the boom. On one side thread the bungee cord through a plastic hook between each set of padeyes, so you have three hooks on the bungee evenly spaced. Then, to furl the mainsail, just reach over the boom and attach the hook to the bungee cord on the other side... Voila... fast easy furling.
Here's a diagram of the setup on my boat. The boom is about 12' long, and I started in about 1" from each end.
I used stainless steel rings at the ends of the yellow and green lines instead of blocks, to reduce weight aloft, while still reducing friction and chafe a bit. The green line section was left long enough so that I can douse the lazy jacks and run them forward along the boom and up the mast—which basically makes them invisible.
Total materials used:
140' of 3/16" line (this is a guess... don't remember exactly how much line I used, and had a bit left over.)
10 stainless steel padeyes (two were attached to the mast for the blocks for the main lazyjack line)
16 3/16" stainless steel pop rivets (could have gone with aluminum, but had stainless aboard)
20' 1/4" shock cord
3 nylon bungee cord hooks
6 1" x 1/4" stainless steel rings
2 Harken micro blocks
Total cost was less than $150 IIRC.