Finally came around to give AB-Solution a try... but unfortunately, it appears like it does not work for my configuration.
The router I am testing on has two VPN Clients, and yes, both have routing rules.
After following your guidelines and with both clients DNS set to 'Strict', I'd notice that when running a DNS leak test, the DNS servers set under the dhcp-option DNS..., of the first VPN Client custom configuration, were also appearing as the DNS servers for the second VPN Client, even though it had its own dhcp-option DNSs...
Any thoughts?
Thank you!