This is not yet possible. There are possibilities to tweak the cost that we have not made public as we are not sure if and how we should make them accessible.
Additionally we currently tweak our routing engine (also based on your feedback - it is not forgotten 
) so that if there are two routes with nearly the same time but significant different distance, the shorter route is picked.
In general using the shortest route does not make much sense for car even if the customer says this is required. There are always some (hidden) costs for time
This example illustrates a bit what I mean:
- shortest, 14.9km, 45min, https://graphhopper.com/maps/?point=49.834882%2C11.550064&point=49.932329%2C11.559677&vehicle=car&weighting=shortest&ch.disable=true
- fastest, 25.1km, 20min, https://graphhopper.com/maps/?point=49.834882%2C11.550064&point=49.932329%2C11.559677&vehicle=car&weighting=fastest
- short_fastest (close to shortest regarding the distance), 15.6km, 28min, https://graphhopper.com/maps/?point=49.834882%2C11.550064&point=49.932329%2C11.559677&vehicle=car&ch.disable=true&weighting=short_fastest&short_fastest.distance_factor=0.2
- short_fastest (close to fastest regarding the time), 19.7km, 21min, https://graphhopper.com/maps/?point=49.834882%2C11.550064&point=49.932329%2C11.559677&vehicle=car&ch.disable=true&weighting=short_fastest
IMO “shortest” does not make sense. Not from the picked route (detour through villages with small streets) and also not from the much longer taking time (over 2x the fastest route).