I am working on one now, tediously. It doesn't seem hard to open the seams on the back, as I use my finger and a piece of wooden clothespin. Also, a lineup of weighted clappers.
Where there's trouble is in butting two of those seams together precisely. One byOne has suggested a tape, and I'm in the process of getting it. Until I have it, I hand-baste every intersection, and they meet perfectly.
I do like the flatness of open seams, but I'll sure be more careful about the pattern next time!
hugs,
charlotte