Great stuff! I've often wished for an easy way to attach that type of bag to the bike, I love what you've done with them!

I might try a variation on this:

I'm theeenking... it might be easier in the shop to carry them one-at-a-time rather than permanently stitched together - maybe instead of cutting the straps, stitching a loop into each and attaching them with a carabiner or keyring or something.