I've added the stitching and seams now. I used Mudbox's ability to paint bump maps for these. I made a series of stitch and seam stamps, set the paint brush to have quite wide spacing, made the stamps follow the stroke and turned on Steady Stroke. It's basically the same process as using the sculpting tools, but no need for a super high resolution model.
It was surprisingly straight forward and successful. I was quite pleased with the results. Then it was just a question of converting the black and white bump map to a normal map and overlaying it on the main normal map.