I've looked in the folder and it seems that unemployment may help migration. Could I overproduce beaus on the mainland to have then go there? (Playing as Italy and trying to make Java a state)
This ought to be possible, but isn't.
i) bureaucrats can't be unemployed
ii) bureaucrats demote on migration (and generally this will result in them reverse assimilating too, so an Italian bureaucrat turns in a Javan farmer on arrival)
iii) significant unemployment provides a modest incentive to emigration, but modest unemployment completely kills immigration
Java is difficult anyway, the last time I turned any significant numbers of colonies into states was 1.2 and it may be impossible with a later patch than that.