I think you need to be a bit more patient... your request was made at 3am British time... most of the forum regulars were asleep

As far as I know land segments are allowed within the same zone by BMI.. as BKK, SIN and CGK are in the same zone this routing should be fine (in theory) - however, the best way to double check is to ring the ICC and see... maybe try a few agents if the first doesn't allow. I can however see this as being something where an agent could require you to pay with two 1-way awards... as this sounds less like a connecting flight and more like two 1-ways from one viewpoint (i.e. a z8-z7 and z7-z7), especially if the dates are quite far apart... so perhaps be prepared to try a few times and probably best if you do segment by segment etc...