How to add a speed factor?

Hi all.
In the GraphHopper Route Optimization API you can specify a speed factor to adjust the driving times. In the open source version, is there a better way than using the inverse speed factor value in the VehicleCostParams.perDistanceUnit parameter? Eg, if the speed factor is 0.8, set the distance cost to 1.25?

So that didn’t work.
Next, I tried using a time multiplier, which did work. But I had to create a wrapper for FastVehicleRoutingTransportCostsMatrix that does

@Override public double getTransportTime(Location from, Location to, double departureTime, Driver driver, Vehicle vehicle) {
	double time = matrix.getTransportTime(from, to, departureTime, driver, vehicle);
	if (vehicle != null) {
		VehicleTypeImpl.VehicleCostParams costParams = vehicle.getType().getVehicleCostParams();
		if (costParams.perTransportTimeUnit > 0)
			time *= costParams.perTransportTimeUnit;
	return time;

Anybody knows a simpler way? Or one that doesn’t overload the meaning of the per-transport-time cost?