Maybe you should find a different pro shop.

I have used a loop for over ten years now and I will never attach a release directly to the string. It is no more dificult to attach to a loop than it is to the string. I don't even have to look at the string to connect to the loop it's just as natural for me as it is for others to the string.

With the mongoose simply shorten your release one hole and you should be good to go. Even if you do loose 1/2 inch of draw how much speed does that really account for? Maybe 5 fps, but then you gain it right back since the loop weighs less than the brass nocks you had on there before. Assuming you used brass nocks.