CO is pretty flexible in the routing rules.
You can have the flight follow illogical routings and be somewhat circuitous so long as you stay in the same award zone. Flying home from Spain via PRG, FCO or ATH should be fine for any connection under 24 hours as long as you can find the inventory.
And remember that you get one stopover and one open-jaw so you could do WAS/BWI - (XXX/YYY/ZZZ) - NCE, BCN-PRG, PRG-ATH-FCO-FRA-WAS/BWI and as long as the time in ATH, FCO and FRA is less that 24 hours you should be fine.