Gin is essentially ethyl alcohol flavored with Juniper Berries (there are different types, but the Juniper Berry needs to be the predominant flavor for it to be called Gin).
I suppose you'd be making a Juniper Melomel (or Methyglin?). If it were me, I'd make a plain old mead. Once fermentation completed, I'd add a muslin bag with some crushed juniper berries. I'd taste it every so often until the desired flavor is reached. Then, remove the berries, clarify (if necessary) and bottle.
I haven't been doing this very long, but, based on the wealth of information I've read through here and at gotmead.com, that's what I would do.