I dunno; what you're asking for doesn't really make sense. If the actual chroot is put into user2's .shellrc, he could exit out of it whenever...?

If you want to get back out to the main filesystem, a chroot isn't what you want. Think about this - it's designed to limit users. Conversations about how to get out of a chroot are typically discussions of why you shouldn't be relying on this for security, not how to add more functionality to it.

Agree with karamarisan: what the OP is asking for makes no sense.
Either you want user2 jailed or you don't
In either case, don't even think of putting him 'under' another user.
Give him his own user.
If you want him to usually be a normal user, but sometimes needs higher privs, you should be looking at sudo.

Thanks all.