BLE mesh Provisioning
Unfortunately, the unprovisioned devices have to be within range of the provisioner in order for the provisioning to work. The mesh specification defines two types of provisioning:-


Advertising bearer 
GATT-based bearer


In the former, the provisioner has to detect the adverts of the unprovisioned device in order to add it to the mesh network. In the latter, the provisioner has to connect to the unprovisioned device and use the GATT profile to add the device to the network.

You can find more details about this in Mesh Profile Specification 1.0, Chapter 2 Mesh System Architecture, Section 2.2.3 Adding devices to a mesh Network.

As for your case, if the device is not within range, the only solution would be if one of the nodes that is within range can become the provisioner and add the unprovisioned device to the network. However not all implementations support this and that will depend on the stack/vendor.

I hope this helps.