The references are, as I understand it, for security reasons rather than character references. So I suppose they are quite lenient e.g. GPs, dentists, etc. would be some options.
I'm not at the stage of applying for sponsorships yet but would have to have a real think about people I've known for 5 years what with, like you say, moving about with uni/work.
Maybe someone has more info...?
V1R