If you didnt need the holster to quickly detach you can just undo that strap that you have the adapter on and then run it through the holster and back through the buckle. Thats what I did with my rangefinder case and bino case.
Pyroducksx3, I was i little hesitant to undo the strap for fear of messin it up when i first got the pack. I ordered the holster adapter thinking it would be much easier to put on and take off, but after getting brave enough to undo the strap on the waistbelt i have to say it is just as easy to attach a holser the way you mention. It is a little tricky getting that strap undone and then back together, but i will be carrying my 1911 the way you mention because my holster for that gun only has 1 1/2" belt loops. The holster in the pictures has a loop for a 2" belt so i will use the adapter for it. Do you know why they put velcro on the back side of the strap on the hip belt (just wondering)?
Cali_hornhunter, Just make sure your holsters have a 2" belt loop or the adapter won't work. I have to admit i somehow missed that when i ordered the adapter (even though kifaru plainly states that on thier website), but it works for some of my holsters so its not a total loss. If your holster has a 1 1/2" belt loop, then i would just attach it like pyroducksx3 recommended as it isin't any more difficult to do it that way.