I think you could do it but it would be tricky.
BA Executive Club members "resident in the Far East" earn Asia miles but I believe you still earn BA tier points. Cathay's miles scheme is Asia Miles (I think).
Therefore you should be able to put the miles to Asia Miles and the tier points to BA if you change your residence to "the Far East" i.e. Thailand if you have an address there.
However - I haven't tried this as a household account and BA Amex means I am firmly rooted in the UK (despite not actually living there so much just now).