Thanks a lot to Maligned for revealing this secret.
Necessary steps:
1. run the necessary amount of dosbox instances
2. connect the instances to eachother with ``ipxnet startserver`` & ``ipxnet connect localhost``
3. from all instances, run setup.exe with -dp param, e.g. ``setup -dpSPPK -level1 -monst``
4. specify the amount of players and start the network game
Additionally, I arranged this little demo player program to make otherwise tedious process be a matter of two clicks: WangBang Demo Player
...and began work on WangBang Demo Archive: https://desomorphine.ru/sw/demos/