get a couple small buckles like these
http://milspecmonkey.com/store/hardware-diy/126-itw-1-repair-buckle.html
Or if you want to get fancier, these
http://milspecmonkey.com/store/hardware-diy/137-itw-surfacemount-1inch.html
attach them to the small loops next to the carry handle, probably with paracord, seen in your picture.
Get some 1 inch webbing and run through the buckles and down through the d rings on your med kit.
That way you can unbuckle it from your pack if necessary just leaving one half of the buckle attached near the carry handle. This would allow you to easily open the pack all the way or remove it completely. I've never done this but seeing your situation, that seems like the most logical way for me.
PS, apologies for the delay, been on vacation.