Indeed I was thinking about break the cardboard down to little pieces so to facilitate the work for the worms but I wasnt thinking about the watering issue. I thought the cardboard would keep the heap moisted so I wouldnt have to water it too much.. isnt this one of the good properties of the sheet mulching?
I think it would work. Also, I'd recommend putting kitchen or veggie scraps on top of it to further attract decomposers like worms and to break up and aerate the pile.
I put down cardboard and filled the rest of a raised bed with enough soil, compost, and mulch material so that I could grow my garden in the added soil. I did this because I wanted to smother the bermuda grass below my garden area. The next year the cardboard had decomposed enough that roots could penetrate the soil without having to compete with the grass.