Yes! This is one of the most common uses of our WAN Balancer app. You can set this up in WAN Balancer > Route Rules. Here's an example of a rule you'd use to direct all traffic from 192.168.100.25 through the 'External' WAN interface:
Bear in mind that the specified host will always use the designated WAN, so unless you're also using WAN Failover, that host will lose connectivity if its designated WAN goes down.
If you'd like only the specified hosts to use WAN B but leave all other traffic on WAN A, you can set your weights in WAN Balancer > Traffic Allocation to 100 for WAN A and 0 for WAN B. Any hosts without specific Route Rules set up will be directed through WAN A.