Thank you for all your input. I'm beginning a new job that will require some frequent travelling so the Ruby is really just for me to cut the check-in queues as they can be pretty long for MH.

I searched on BA and found KUL to USM (Koh Samui) which is operated by Bangkok Airways. But spoke to both travel agents and BA directly and they wouldn't sell it to me as it would need to be a international connection presumably only to/from LHR so seems like no more options for me