How to limit bandwidth on a 4G failover link

[politby]

Hi y'all

I have 2 fast ISP connections WAN1 and WAN2 (same ISP but different contracts so if one fails so does the other) . I also have a 4G connection via a Huawei router connected to pfsense.

I have set up a gateway group where the 4G acts as failover for WAN1. WAN2 has no failover.

If WAN1 goes down I don't want the data cap on 4G to be instantly used up by some streaming or other bandwidth application - essentially I'd like to limit the 4G connection to low bandwidth stuff like email.

So I have a firewall rule that forces known bandwidth heavy hosts to always use WAN2, which doesn't fail over. But that's a non-precision approach as it just cuts off those nodes. Can I do this in a smarter way?