I exchanged some Email with a colleague about your inquiry. We don't think NanoRoute has an explicit option to ensure that connections are never made with vias. Could I ask why you're seeking to avoid this type of connection?
If you're trying to avoid notches, you might instead ask that vias are entirely within the pins (with "setNanoRouteMode -routeWithViaInPin true"). If you're seeking to avoid minimum area violations, you might find that "setNanoRouteMode -drouteViaOnGridOnly" forces NanoRoute to place vias far enough away from the pin that minimum area rules are satisfied.
Thanks for posting this question! I hope this helps.
PS In the future, you'd probably find faster responses to SoC-Encounter questions in the Digital Implementation area.