Park them on the `grass`...they are `tactical `aircraft after all...
Having visited Airbus at Seville on numerous occasions, I can vouch for there being very little in the way of spare grass on which to park grounded A400Ms. Not only is the Airbus side of the facility pretty much completely paved (and I assume it is this area that is rapidly filling up), but the facility abuts onto the international airport which would again limit room for overspill.