can they play in a minor league stadium? Perhaps Portland or Salt Lake sort of as a tryout for a follow on expansion team? Wild idea - why not Montreal? It'd mean division shifting, but they have as major league a stadium as RFK was.
There is an AAA stadium in Las Vegas that seats about 10k but using it would create logistical problems for the team currently playing there, and the A's would probably prefer to have a bigger stadium. I've also seen reports that the MLBPA would oppose playing at a AAA park.
There has also been talk about sharing the Giants' stadium in SF for a few years but the Giants and A's ownership do not have a good relationship from what I read earlier.