Make that "Put the avocado in a greenhouse (outdoors) and continue to keep Biggle indoors?" if that's clearer.
(You probably don't have to worry about Biggle getting mastitis (http://cal.vet.upenn.edu/poison/plants/ppavoca.htm) as much as goat owners do, and if he's puking it up promptly that presumably reduces the dose he gets, but keeping it away from him does sound a good idea.)