Folding is easy once you have the space. Perhaps you can take it to a local school gym. Alternately, I have thought about raising it partially using a block as I have an area in my home that is two stories. Also, with no wind I was able to flake the 135 onto the deck well enough to stow it into the bag. You just need someone else to lower it slowly while you keep tension on it and impart the flaking. I tried flaking my main on the boom (fairly easy to do on a smaller boat by starting at the back, pulling on the sail and imparting the flakes...bit tougher on a 35 footer), tying it in multiple places (it is loose footed) and then sliding it off. It would probably work well for an older main, but mine is only a few years old.
Lay it out on a clean surface. Fold up up the bottom about 18 inches then start flaking it in similar lengths until you get to the headboard. I had socks on and found that walking back and forth to smooth the folds worked well. Frequent neatening of your flakes is necessary too. One extra fold at the top to put the headboard inside the bundle then start at the luff and just roll it up tightly.