Suggestion:
Open up away tickets very early. No preference selection.
Based on this the club decide which allocation to take.
All those who have already bought get 24 hours to choose their seats, if they don't seats are allocated to them on mythical 'best' basis.
Tickets go back on sale.
Ticket staff deal with some moving around requested by those who already bought who didn't pick their seat during the initial window.
Open up away tickets very early. No preference selection.
Based on this the club decide which allocation to take.
All those who have already bought get 24 hours to choose their seats, if they don't seats are allocated to them on mythical 'best' basis.
Tickets go back on sale.
Ticket staff deal with some moving around requested by those who already bought who didn't pick their seat during the initial window.