After seeing lots of questions like Please don't migrate low-quality questions to other sites I realized that I don't really know the rules for questions on those other sites.
I figured that most likely the people who vote to migrate never bother to click on the FAQ links on the migration page. I know I never do.
Maybe you could prevent inappropriate migrations by putting a tooltip (like the tag wiki excerpts) on the radio button you have to click on to select the migration path. By allowing the moderators for the site being migrated to to specify the text of the tooltip, they can tailor the wording to the specific problems they see with the questions being migrated.
For example, on the migration path from SO to P.SE, the tooltip might be like:
For programming questions that don't involve code. While subjective questions are allowed, the must be constructive and not just mindless fun.