Yes it is, if you are willing to run a shell script on your router. The command
nvram set opvpn_cfg='
client
remote xx.yy.ww.zz
....
<ca>
---------BEGIN CERTFICATE--------------
...
--------END CERTIFICATE--------------
</ca>
<key>
....
'
will create your config file, which you can start as follow:
mkdir /tmp/openvpn
cd /tmp/ovpn
nvram get ovpn_cfg>ovpn.conf
mkdir -p /tmp/etc/config
echo -e "#!/bin/sh\nkillall openvpn\nping -c4 localhost\nopenvpn --daemon --config /tmp/ovpn/ovpn.conf">/tmp/etc/config/ovpn.wanup
chmod +x /tmp/etc/config/ovpn.wanup
openvpn --daemon --config ovpn.conf
This command will stop the OpenVPN:
killall openvpn
If you wish, you can put the above commands into a script file, and have it executed at boot:
nvram set rc_startup='mkdir /tmp/ovpn
cd /tmp/ovpn
nvram get ovpn_cfg>ovpn.conf
mkdir -p /tmp/etc/config
echo -e "#!/bin/sh\nkillall openvpn\nping -c4 localhost\nopenvpn --daemon --config /tmp/ovpn/ovpn.conf">/tmp/etc/config/ovpn.wanup
openvpn --daemon --config ovpn.conf'
These are rather generic, but you should be able to mold these as per your needs.