This isn't supported with the "spectre" netlister either - you must be using the obsolete "spectreS" interface?

In theory you could add bn support with a custom AMS  netlist procedure (I've done the same for transition of existing spectreS based designs to spectre, with the view that any new schematics should use the inherited connection approach). I've not tried this with AMS though, but it ought to be possible.

However,  remember that netSets do not have to be on every instance - if all instances in a block have their bn set to (say) vss!, you can put the netSet on an instance of the block (or even further up the hierarchy) and all child instances will inherit the netSet. In essence a netExpression can be resolved by the first netSet found looking upwards in the hierarchy. Put another way, if every single 3 terminal device is connected to the same net, you could put a single netSet on an instance of the top level block, and that would work.

Of course, if you have individual overrides, you'll need to handle that, but for most cases people use 3 terminal devices where the bulk is connected to a supply or explicit bulk connection into a block; if they want to wire it to a local net, they'd use a 4 terminal device to make it clearer in the schematic (at least, this is good practice - there will always be cases where it doesn't get done like this).

Regards,

Andrew.