I was browsing for some tights and found these:
http://www.wiggle.co.uk/asics-top-impact-line-tight-aw12/ They look as if they have a rear seam that might do what you want :D The highlighted seam stitching might distract attention away from your crack, but you would still know / feel it was there!
There is a good selection of tights at the Wiggle main page:
http://www.wiggle.co.uk/mens/run/running-tights/ I'm sure there's something there for you ;)
PX