You can keep them physically separate. Or you could use an export bus on my main network pointed to an interface on dimlet network so that any dimlets in the main network automatically get moved to the dimlet network.
But just use a single ME drive with enough 1k disks and an interface terminal attached to it. Run some type of ME cable from main network to it. But place a quartz fiber in the cable someplace. That will provide power to the drive and terminal but neither will show on your main network. BTW: since the quartz fiber blocks the ME network this just uses power and not a channel from your main network.
Oh and don't use an ME chest. It can't hold enough item types (different dimlets).