Hi Tim/Colin,
Bets option to achieve this to use custom program. I got the same requirement from my client a year ago. Custom program was used where, in material master WM1 view we have used the capacity usage field for minimum order qty to replenish as well as when creating TO there was logic built for sorting LQUA table in descending order of Available qty. Hope this somehow helps you and give an idea of goiong forward.
Regards,
Pritt