How about the following framework:

V2G framework - used to set mode, set current/charge limits and query status  with commands such as,

V2G mode - used to set mode either V2G, G2V, REM (default - mode remotely set by charger/V2G/V2H unit) 

V2G limit - used to set limits such as charge/discharge current limit and SOC min/max limits

V2G status - used to report mode, limits set and power/current flow

V2G start - used to start powerflow in a given mode 

V2G stop - used to stop powerflow 

The basic wrappers could be defined in vehicle.h/cpp and the feature confirmed as supported in the specific vehicle and coded to implement the specific command features.

Views?

Cheers Derek