On some of my bikes I use the Thorn accessory T bar, some bikes I use a second threadless stem with a stub of cut off handlebar. At one time I tried PVC pipe instead of a piece of metal from a handlebar, but it cracked and made a mess of things, I do NOT suggest PVC pipe for that.
For me, a second stem is usually a lot cheaper, as the shipping cost from SJS to me in USA is not cheap. But when I bought my Nomad Mk II, the Accessory T bar was in the box with the frame. Later I added a Thorn Accessory T bar to my road bike.
My goal was to get the weight in the bar bag lower and as close to the steering axis (steerer tube) as practical. And a minor advantage was also that I have more real estate on the handlebar for GPS mount, bell, interrupter brake levers, etc., if there is no bar bag bracket on it.
First photo, a second stem that is an adjustable stem.
Second photo, second stem on my Thorn Sherpa, I also have a wrist watch type heart rate monitor on that stub of handlebar and that is on a wrist watch to handlebar adapter, that might make the photo a bit confusing.
Third photo, 55mm Thorn accessory bar on my Nomad Mk II.
Fourth photo, 55mm Thorn accessory bar on my road bike. This was the only option on this bike as the bike only had 25mm of spare steerer tube when I bought it.
I also have done this on my randonneuring bike. And I have removed it from my road bike to temporarily attach to my folding bike. But four photos is enough.
On my road bike, the brake cables are less than fully convenient with the bracket. That bike came with a much lower stem, I changed the stem to a 35 degree stem, which also made the cables a bit shorter than ideal. But I do not see a real need to add a bit more length to the cables yet.
I am starting to see a reason for a fifth photo.