Answering my own question, I would say the best way of implementing SPLIT, for Stand Alone mode with the DUO controlled by SW2, with what CAT commands etc are at hand for the moment, is making two macros:
This macro disables split mode and enables VFO A for tuning around searching for stations. It is necessary to disable split mode since it is not possible to do VFO A = VFO B while in split mode.
This macro enables VFO A and SPLIT mode. It's necessary to also enable VFO A for listening on the RX frequency since manually pushing A=B on the DUO always presents/enables VFO B as a result.
Operate like this:
Working split mode easily with SW2 in another question. It is too akward today. Let's hope for an easy-to-use split functionality in SW2 in a future release.