How about stitching up to the belt loop, back stitch. Lift the foot over the loop and proceed to the next one.

The trick would be don't go over the belt loop go under. Stitch up to the belt loop, lift the loop, stitch under the loop as far as the loop will stretch then end your stitching. Now, start stitching again on the other side of the loop.

I usually take out the stitches on the bottom edge of the belt loops then stitch them back when done sewing the lining. You could also use fabric glue to fasten the lining

Good idea.

Why not make a removable bag for the liner? This way you can just pick everything up to move to another bag. You could have a whole set of bags with one interchangeable liner. :o) Ann

Nice bag. I have some jeans to make a purse out of so your post is very interesting and informative. Sorry I can't help you.

How about sewing it on by hand. It shouldn't take that long. Good luck! Love the bag.

Can you take it to an upholstery shop and have them sew just that seam for you? We get such requests often and seldom charge (but I can't speak for other business owners).
I like the suggestion made to sew up to (and under if you can) the belt loops, then continue stitching on the other side of the loops. You can hand stitch by hand just those areas missed.

You could hand sew loops to the inside and sew buttons on to apply loops like the yellow pins are in the picture otherwise you will have to take the stitching out of the bottom of each loops to sew the lining and then re-attach the bottom of loops. However the jean purse is adorable. You can even attach a few appliques and bling for the next ones you make lol

How about heavy heat-n-bond