Random, potentially useless thought (I don't know the details of the HSBC->CCB trick): know someone in SIN (me!) who prepaid 2y worth of taxes, for self n missus, when the DBS gig of awarding miles for payments via AXS kiosks (including taxes) was going away..

3y back & it was a LOT of miles (both being reasonably high earners- don't recall the details but was 1.2-1.6mi/S$, & the machines could only process 10k/transaction)..The IRAS even offered to refund the excess payment via cheque (we were both on the monthly interest free payment plan, that makes sense here in SIN)...

ETA: in the second year they actually refunded the excess (my estimate - actual), to our respective bank accounts.