Elmer's Glue.
I've done this with borders many times - and the end result is always worth the effort.
I personally find non-matching patterns on borders very distracting.
My eye always tends to focus right in on it.
But that's me.
It's similar to the way I do the corners with multiple mitered borders - especially ones where you want the fabric patterns to match up.
For borders (and backings, too, if you want) - you didn't mention which it was for.
(Actually, even if you needed to match smaller pieces for use within the quilt top, this would work as well.)
Match the two pieces up with an inch or so overlap.
Then turn one of the matched edges under, making sure it's straight and even across, and then press for a sharp edge.
Overlay this on the other piece until the pattern/design matches up perfectly.
You can pin it a bit further back to stabilize the two pieces if you want. I did that the first time but haven't since.
I then put a thin line of glue under the edge (really, it could be on the folded part or the 2nd piece of fabric ), and then wiggle the two pieces to make sure they're still matched up.
Press where the two pieces meet to set the glue.
Gently fold back the top piece (the one with the pressed seam) and sew on the crease line.
You can baste it first if you want to make sure and then go back with smaller stitches once you're satisfied it's exactly how you wanted .
Trim the seam allowance back to 1/4", and now you have one piece of fabric with a continuous flowing design.
I used the same method on this quilt matching up the seams in the corner blocks and mitered borders:
http://www.quiltingboard.com/main-f1...ml#post2521413