The 4800 and 6300 pack bags, wrap easily around the frame and connect together. I usually slide it under the load lifter webbing. The 3900 can , but it takes more effort and I don't do it. Normally, I repurpose a compression strap if need be, but that is rare. On the Evo, the lower frame attachment point at 24 inches has a buckle on it for that purpose, however if you use the frame at 24 then you loose that. The assumption is , at lower heights , you will not necessarily be "hauling" and thus can use one of the compression straps easily. Most packs, use some arrangement of 2 compression straps. We use 3 as standard, so even if you repurpose one, you still have two.
You don't also really need to loose a compression strap either. There is another method which is to put two buckles on one strap, the first goes up to the roll top, the second down to compression. There are some limitations when doing this, mainly webbing length. Overall the compression system is very very adaptable.
Alternatively, the more exposed frame of the Unaweep opens it up to a lot of adaptability. A triglide, buckle and some webbing and you just added another compression strap. Likewise, you could make a mini prusick and put on the frame and attach whatever you see fit.