Removable momentum bivy top thing?

Does it really need to attach to the inner? Since you already have a floor, why not enclose the foot, then wrap it under your pad and attach the opposing sides with cord ala Nunatak Arc style?

Well, that would work, but the idea is that it would just drape over me and I wouldn't have to worry about keeping it tucked under due to the chords. I use a quilt, so if it's cold enough that I want the momentum, I probably won't want the hassle of tucking both everytime I roll. It shouldn't really have to be any larger with the chord set up than it would be wrapping it, maybe and ounce or so heavier, but hopefully more convenient.
It's probably hard to visualize by my vague description.
Thanks for the idea though.

why not just use a wider quilt that offers full coverage and makes an extra layer of m90 un-needed?

-Tim

Well I've already got a perfectly good quilt.
I've got a bivy as well.
I'm going to be doing a big section of the PCT, and I'd like the extra bit of warmth from a bivy, but rather than mail one thing home and have another mail to me then reverse the process after a while, I'd just like to mail one item home.
Maybe I'm just making this way too complex…