If so, you could try this:

1) Raymarine Seatalk Converter Kit http://www.defender.com/product.jsp?path=-1|344|302025|296558|1033212&id=1787959&cartId=3237595 in combination with this

2) Raymarine Seatalk NG To NMEA2000 Adapter Cable http://www.defender.com/product.jsp?path=-1|344|302025|296558|1033212&id=1108756&cartId=3237600 and this

3) Lowrance NMEA 2000 Network Starter Kit http://www.defender.com/product.jsp?path=-1|344|302025|320633|762896&id=1296950

The real question is whether the Fluxgate will give you an NMEA HDG sentence that can be delivered to the NMEA 2000? I'm pretty sure that's the NMEA sentence what will enable the chart overlay function. I also think there's at least a 50/50 chance it would work, because I can now also see the other Raymarine instruments on the HDS display and should be able to drive the AP now from an HDS course (not that I would do that, but I might try to see it it can steer to an active waypoint).

You might want to call Lowrance support and get their take on it.