OpenWrt+Multiwan. How to force the router not to change wan during one session?

Question

Load balancing

There is a router with OpenWrt Chaos Calmer r42230 on board.
Installed multiwan with load distribution for 2 providers using netfilter (Fast Balancer is the best distribution) .
Is it possible somehow to force not to change wan during one session, for example, in a personal account.
During authorization, if ip changes, it often throws it out.
Of course, you can create additional a rule for a specific site or ip address, but this is a crutch, you can’t create rules for everything.

Answer 1

Taki decided to spend money and buy a gigabit mikrotik with Router OS on board, everything should be more thought out there.