1) Replace the M8 bolts in the ends of the fork with 8mm "set screws" 30mm in length. Then you can use 8mm wing nuts to tool-lessly secure the bag on or remove the bag from the fork tines.
2) Replace the M6 bolts that attach the fork to the handles mounts with 6mm set screws 20mm? 25mm? In length to allow you to tool-lessly attach/detach the fork to/from those mounts using 6mm wing nuts.
If you always remove your bag from your F-15 when you leave your bike, then (1) has no real downside. Just keep the wing-nuts in your bag.
Unless you remove the fork from the handlebar clamps regularly, then (2) is not really useful. Even then, well it just means you don't have to have a 4mm Allen wrench to do something trivial. And, depending on the mount of the clamps to your bar, attaching/detaching the fork can be somewhat tedious with the set screws since they stick up all the time. (That's why shorter may be better.) Additionally, the wing-nuts do make the fork easier to remove for thieves (more likely vandals). That said, it's nice not to have to find that tool all the time if you remove the fork often.
Set screws are simply fully threaded pillars with socket inserts on one end that an Allen wrench can fit into. As an example, see the metric set screws and wing-nuts at BoltDepot online.
Oh, and the cotton shoulder strap offered by Laplander Bags works really well with the BarSack. I can't remember if my BarSack came with a shoulder strap or not. If it did I'm pretty sure it was nylon. Which is okay and fully functional. I just really prefer the feel of cotton, even though nylon takes up less space and probably weighs less. Surely relative strength isn't an issue for the BarSack or similar bags.
Yours,
Thomas Lynn Skean
Yours,
Thomas Lynn Skean