While it can theoretically be done with scratchbox, as a matter of policy I don't port to environments I don't have because of the support issues that would be involved. Right now, for example, I'm working on 2 obscure bugs, each reported by just 1 user, that are difficult enough even with the right hardware, and would be even more difficult without it. As I don't have an N900, I'm not working on a Maemo 5 version.