Solo X/C is PIC time, though bear in mind your CFI will have to endorse your logbook for every single destination (
AFAIK).
The FAA also has a funny little thing called "performing the duties of Pilot in Command". This is mainly used for the ME ratings where the FAA realises that no one in their right mind would rent you a twin to get PIC hours without a rating. Not sure if it could also apply in your case in a single, so you could actually get "PIC" hours with an instructor onboard somehow.........probably not.
Wasn't there a 13 year old girl who flew across the USA a few years back?