Well it should work…
IP mangle.
new routing mark-bypassvpn source-address-list =(list created in IP firewall lists to identify which IPs) “bypasslist” chain=prerouting
IP route
destination=0.0.0.0/0 gateway=gateway_IPaddress_ISP1 mark route=bypassvpn
maybe try a two step mangle rule
First step marks new connections for those source LANIP addresses.
Second step route marks them.
and then make the necessary route rule…
Maybe this two step is unnecessary but maybe more efficient??