Let's assume it is required in general case.
I tested both Ethernet and Wi-Fi and neither one works.
# ip route get 1.1.1.1; \
> ping -c 3 1.1.1.1 &>/dev/null && echo OK || echo FAIL
1.1.1.1 via 192.168.8.1 dev tun0 src 192.168.8.3 uid 0
cache
OK
# ip route add 1.1.1.1 dev wlp2s0; \
> ip route get 1.1.1.1; \
> ping -c 3 1.1.1.1 &>/dev/null && echo OK || echo FAIL; \
> ip route del 1.1.1.1 dev wlp2s0
1.1.1.1 dev wlp2s0 src 192.168.1.146 uid 0
cache
FAIL
# ip route add 1.1.1.1 dev wlp2s0 via 192.168.1.1; \
> ip route get 1.1.1.1; \
> ping -c 3 1.1.1.1 &>/dev/null && echo OK || echo FAIL; \
> ip route del 1.1.1.1 dev wlp2s0 via 192.168.1.1
1.1.1.1 via 192.168.1.1 dev wlp2s0 src 192.168.1.146 uid 0
cache
OK
Tested using the UCI configuration, the route is added without gateway and it doesn't work.