mmmm I'm 6'7" and manage just fine on the Sport..... I didn't think the ergonomics of the Breva were vastly different...
On long rides -and I've covered 1000km in a day once or twice, a sheepskin gives you some separation from the seat and a 1/2" lift.
With hard panniers on, I can still use the rear pegs (feel like rear-sets as Tony suggested) to vary the angles a bit.
I've tried a couple of lowered peg sets, but with my size 14/48 boots, I couldn't find a set that worked around corners...
Stopping more often might do it, but the 440km tank range doesn't help that...
Selling = no
Raise the seat = maybe
Lower the pegs = research required
Surgery = Braziliaan butt lift
Stop more often = if you do sell and get a GRiSO, this will occur naturally