No recent direct experience personally but I can, for example, look at using my 241 on LHR-SYD and I am offered the option of a stopover in SIN. So I know it can be done for that route. Hopefully someone else will be along shortly to confirm (or otherwise) what other routes it can be done on - based on recent experience. I think the issue you may encounter (apart from availability) is the inability of either BA’s system to handle it, or speaking to an agent who does not know how to press the right buttons. If the latter, then best to HUACA IMHO.