If we had coin denominations (like this), where value of coin depends on ID of coin, farming could select range of IDs where average coin value is the desired farming reward.
Mechanics: As master nodes select coin ID for farming attempt, they discard if it’s not in the right range, try until one is in the right range. They can use a serial number (like a nonce) for generating the hash for the coin ID to make the search deterministic.