Thank you for your reply.
Our LAN network is 192.168.1.0/24 and the remote LAN is 192.168.90.0/24.
I have a site to site VPN NATed from our Checkpoint to a OpenVPN server (192.168.1.2) in the LAN with another OpenVPN server on another site.
At first, I've configured a static route on the Checkpoint (192.168.1.1) to route all traffic from our LAN to 192.168.90.0/24 through the local OpenVPN server (192.168.1.2). at this point I was able to ping 192.168.90.0/24 from LAN but couldn't SSH or connect on any other port. (Probably due to ping redirect, since 192.168.1.1 sent me to 192.168.1.2 on the same LAN).
When I added a static route on a client (192.168.1.159) to send traffic sent to the remote LAN (192.168.90.0/24) directly through the OpenVPN server (192.168.1.2), I've got a full access to 192.168.90.0/24.
I want to prevent configuring client by client with this static route so I thought to push it using the LAN's DHCP.