As a longer-term solution, I would suggest adding cross-posting as an explicit *close* reason. This is already being used on [Unix & Linux](http://unix.stackexchange.com), listed under *Off Topic*.

> This question has been posted on multiple sites. Cross-posting is strongly discouraged; see the [help center](http://unix.stackexchange.com/help/on-topic) and [community FAQ](http://meta.stackoverflow.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu) for more information.

It seems to work well. Off-topic, cross-posted questions are generally closed soon after I flag them as such and I think this would be a useful feature for Server Fault.