Well, seems like others had the same trouble but did something about it. Tor Norbye show some screenshots of the latest new Netbeans support for ActiveRecord completion here, which actually does this. Netbeans is looking into the migrations and into the model, and then supports code completion in the IDE with all the information it collects. Supposedly it does not stop at the migration that creates a table, but also recognizes later migrations that change the schema. Things like rename of columns.
Cool! Simply cool!