Some caps I've been able to use our flat hoops to do that, not sure what other's do as we don't do a lot of curve sewing around the back, but when we do I try to push them to a good cap that has a some flex. I'm sure other's will chime in here as there's some really good embroidery guys here DKgrafix and Brandt (Graphicdisorder) to name a few.
darryl