+1. the USGI stuff is designed to be separate. i think it's better than the alternative you're suggesting.
i have a german/bundeswehr pack from the 80s that i love, but the suspension's a little weird due to its ability to have the pistol belt attached along the lower edge, as you're asking about for the US Alice setup. the german y-straps were built into the pack straps, so i have a d-ring between my shoulder blades, and hooks on the lower portion of the pack straps for the belt to clip into.
see the pics below. the first is a german pack on a frame, which i don't have, but note how the shoulder straps are attached up top. it's like an alice on a frame, and would be my prefered method.
the next picture is a set of german y-straps. not a lot different than alice LBE, but i wanted you to see how they're worn by themselves.
the last picture is my pack, which is a varient that blended the two. note the d ring in the middle.... i have cut off that middle strap, but you can see i'm stuck with the d ring. it doesn't effect how the pack rides, but it does get twisted up sometimes. i do not like it.
just carry your alice on your back, and let the LBE straps out long enough that the web belt rides just below your waist. they're easy enough to let up/down as needed.