Posting an answer for the sake of those who may come looking later:

The original question "Is this possible with SQL Server bcp from NodeJS?" remains unanswered.

However, @siggemannen suggested serializing my recordset into JSON, which can then be sent to SQL Server in a VARCHAR(MAX) and turned back into a table value using the OPENJSON function. The columns of this table value can then be processed in SQL as you would when SELECTing from any other table.

This allows efficiently processing datasets at a size that meets my use case.