We recently tried the sleepsack with attached hood over an armbinder with a severe 3.5-inch-tall patent leather posture collar just to top it all off... I'm kind of amazed she could handle the armbinder inside the sleepsack - it's a pretty strenuous position. But overall we have to declare the experiment a success. =0)
The surprising thing is I had extra room on either side of the sack with her arms in the armbinder. I could actually make a more fitted sack (without internal sleeves) to really be snug in the waist area, but it would only fit in that position. It might just be worth it though - it looked incredible!