this sure is possible; every command specified in a config file can also be specified at the commandline by prepending '--' to it, so
server 10.8.0.0 255.255.255.0
proto udp
port 1194
ca ca.crt
becomes
openvpn --server 10.8.0.0 255.255.255.0 --proto udp --port 1194 --ca ca.crt
etc