My LM2000 will cut down 8" from the shroud, but that still doesn't help me with big logs (quartering by your method). What I have done is to actually quarter the log. You can do that with a big chainsaw or by splitting along the grain. [I have split big oak logs with black powder, actually blowing them up - very fun and not as dangerous as you might think (if you know what you are doing - check YouTube - not responsible for accidents)]. Once you have the quarters, just position them on the mill so the cuts are perpendicular to the rings (easier said than done). There are some good threads about quarter-sawing on the Forestry Forum website. It's a lot of work, but sometimes worth the effort.

What type of log are you cutting? THe best luck I've had with quarter sawing is cedar. I cut one end, force in a wedge or three or four, then get a gap that fits my little floor jack. I use that to pry it apart. Then I do the same to the halves. Then, when I put each quarter on the mill, I end up with quartersawn wood. NOTE: If you try this with eucalyptus, you'll end up screaming gibberish to yourself, and with a broken jack. The grain on that wood is absolutely crazy.

The cedar bark dulls the blade much quicker than the wood; as you turn, if you can cut into wood (with the bark on the back side), your blades will last longer between sharpening.
Good luck with the logs. Hope the cedar isn't so big that you can't wrangle it onto the mill!

Just in case you do wind up quartersawing, I generally quarter big logs with a chain saw, like Eddiemac describes. You can also slab the log, and accept whatever quartersawn pieces come out of the middle. Of course this means edging all of the boards, but it will give you a fair amount. Any sawing pattern will give you some quartersawn lumber.