A staple doesn't work. Somebody will sue. Fed's may not even approve it. There hasn't been a straight staple in decades of SLI's. So, lets be realistic instead of thumping chests.

You make the E195/A220 the Gap jet with a fence around it. It becomes the new Group 2. The RJ's become the new group 1. All other existing groups move up one number.

Group 1 fenced from displacing any Group 3 and up.
Group 3 and up fenced from displacing Group 1
Group 2 bids actual DOH.

Fencing protection only for pilots on seniority list at DOS
Once everybody is retired it becomes one lift with no fences.