Assigning from multiple subnets in a container

[#1]

I have a situation where I'd like to assign devices in a single lab, on a single router, to different subnets for organization purposes. For example, the overall subnet might be 10.0.0.0/20, but I want to assign devices A and C to 10.0.0.1/24 (but with a 20-bit subnet mask), while device B is in 10.0.0.0/24 (also with a 20-bit subnet mask). Everything is statically assigned IPs per MAC, so there's no dynamic allocation. When I try to do this, all devices are routed into the 10.0.0.0/24 subnet, which means that devices A and C fail to find their records. Is there a way to tell NIOS to search EVERYTHING in the container, since it's really just one subnet, broken down into chunks?