Redirect specific lan ip(s) outbound traffic via another lan ip (vps client within lan)

I use openwrt router and have a vps client (static reserved ip) in lan.
I'd like to use the vps client to serve as a gateway for specific/some lan ip addresses (reserved one, e.g., NAS) for outgoing (internet traffic).

vps client has ip_forward and also I restrict leak with iptables rules on vps client (it's a raspberry pi).

Previously I set the reserved vps client ip on the devices which I wanted to use via vps client (simply defined vps client's ip as a gateway). I'm wondering if I can make it differently, one level upper on the router the routing.

I'm not very experienced with networking (the current solution works, but maybe not the best), thanks for your patience/explanation if something is not according to the "big book".