I did this all the time in VA for my veggie gardens/pumpkin patches/sweet potato patches/etc...I sped it up by peppering it with compost, then covering it with thick, black plastic and cooking it all summer. By the end of the summer, it was ready for fall veggies...the sweet taters were sort of a sacrifice because they helped aerate the soil without having to double dig it, and they made so many tubers anyway! Add a heavy mulch over the winter, and the next spring, it was ready for planting and remained relatively weed free throughout the season.

The heavy plastic cover sounds like a great speed up idea. If I ever Lasagna again I will use it.