To get a fully featured multi-cell system, you need both network _and_ radio connectivity between the base stations.
However, you can use a multi-site setup, by using the "Allow multi primary" setting. In that case, you will have a primary base station on each "site", and handsets will be able to roam from one site to another with the same registration. Obviously, handover will not work, so you can't move from one site to another while in-call.
For this to work, you have to make sure that both sites can communicate over the network and that they *never* "see" each other radio-wise.
Thank you for the answer