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Gary, You'd have to consider the escape holes to be risers, their dual functions being to ensure there are no voids, and no captive product expansion separating the two halves. I've never worked in a foundry, but have been fortunate to have toured foundries and seen the processes from pattern making through sand and investment castings. It's the same basic tech for everything from jewelry to engine blocks. I would have loved to have been an apprentice under Henry ford's Cast Iron Charlie!
Your idea of pumping through a zerk is useful here, and can be done easily not with a zerk, but simply to use a disposable syringe butted up against one of the holes, which would then function as a sprue.