Brian, you're replying to a ticket that has been closed for over two years, and the topic is unrelated. If the problem persists after my reply, please re-post your question (or follow-ups) on the mailing list.
Having said that, you would have to choose Sample/Restrict by condition, and then enter an expression like "unit != 6 && unit != 8" (without the quotes). If the series "unit" doesn't exist yet, create it with "Add/Panel group index" first (or similar wording).
Whether that qualifies as a "simple way", I don't know.
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