This is the said plan that has been leaked on to DS:BB and The official c4 boards:
1. The eviction will take place as normal, with the winner returning to the main house. The loser will stay in the HND.
2. The remaining 5 HMs will then select the person to join them from the 5 in the HND.
(Apparently Brighter Pictures want to seem fair to all HMs, which is why the evictee is being given the same chance to return as the other evictees. I laughed when my mate said that!)
3. The selected HM will then rejoin the main house.
4. If the latest evictee (Imogen or Richard) is not picked, then they will leave first and have the usual exit interview. Then the other evictees will leave and have a short group interview.
5. If Imogen or Richard is saved, then all the old evictees will leave together and have a longer interview.
The issue of Glyn is unresolved. Some of the production team want him to be sent to the HND and to take his chances with the others, but this might make the broadcast timings difficult. Others just want him banned from the selection process for the returner. This hasn't been decided yet.
Source: DS:BB & C4 Fourms