It might be possible if you don't use raid ID's, but rather at which point they are locked out.
Since we're talking about PuG's for raids across realm, having the same people on the raid is not a necessity. It might be preferable though. Some people will be unavailable at certain times and on another realm. With no crossrealm chat available ingame, it would be impossible to arrange crossrealm pug's for raids with the same member.
If you use the raid progression rather, it becomes easier. If you have defeated the 1st boss for a given raid and you use the raid finder, you will only group with other people that has also done the 1st boss. It might be also possible to group with members that has completed the second boss and are on the third, but with the understanding that you'll miss out on the second boss. Similar to joining a dungeon in the middle.
They could use raid ID's as a preference for selecting a member. For example, a pug does the first boss in ICC10. The next night, some members queue again for ICC10 and the raid finder finds eligible members from the previous pug. They make it up to 6 members, and the additional 4 members are taken from other people queuing but wasn't in their pug.