Let's back up a minute, and talk about two things: (1) how is the "spirit of the rule" going to be monitored?, and (2) what is going to be the punishment for violations?
1) How is the "spirit of the rule" going to be monitored?
The first resource you have is the "Rule 5 Draft Order" page. That lists all teams along with the number of players they have on the 20 man roster at the time.
The second resource you have is the "Player Search" page. You would have to go to that page, search on each of the 32 teams individually with "Level - All" and "View - Status Info", sort by LVL, and the unassigned guys should show up at the top of the list. You then have to look at the "Signed Thru" column for each of the unassigned guys to look for those with future seasons on their contracts (they are the ones not eligible to be exposed to R5). And you have do do this twice for each team, once for pitchers and once for position players. So that's 64 pages you need to look at.
So once you go through these two resources, you should be able to tell how many people are on the 40, and how many people are in the "unassigned" loophole for each team. The total of these two need to be no more than 20.
That seems like it's going to be a fair amount of work, and somebody (either the commish, or a combination of the commish and one or more trusted "deputies") will have to do this on R5 freeze day.
2) What is going to be the punishment for violations?
Shobob, I think you mentioned in the WC that the punishment would be immediate removal from the world. Is that practical? Let's say you have 3 people in violation. Is is practical or reasonable to expect that WIS will immediate remove 3 people from the world the day after the R5 draft, and you're going to find 3 replacement owners willing to come in to take those teams and adhere to the rules? What if it's 5 or 6 owners? I predict that potentially forcing that much in-season turnover is going to be extremely chaotic and create a lot of dissatisfaction among the remaining owners.
Perhaps a lesser punishment than immediate removal would be more prudent. Let's think about alternatives.