How can I configure the energy dashboard to understand my net electric meter?

Configuration
16

Not sure how well this would work but maybe you could use a trend binary sensor an automation, and a utility meter with two tariffs (export and import).

This binary sensor should be on when you are importing energy, and off when you are exporting energy:

binary_sensor:
  - platform: trend
    sensors:
      energy_export:
        entity_id: sensor.your_net_energy_sensor
        max_samples: 2
        min_gradient: 0

This utility meter will create two energy sensors, one for import and one for export:

utility_meter:
  grid_energy:
    source: sensor.your_net_energy_sensor
    cycle: daily
    net_consumption: true
    tariffs:
      - import
      - export

This automation switches the utility meter tariffs:

trigger:
  - platform: state
    entity_id: binary_sensor.energy_export
    to:
      - 'on'
      - 'off'
action:
  - service: utility_meter.select_tariff
    data:
      entity_id: utility_meter.grid_energy
      tariff: "{{ 'export' if trigger.to_state.state == 'on' else 'import' }}"