Jerboa for me: top left button shows a list of account credentials stored in Jerboa. From this you can switch from one account to another, or to "anonymous". If you sign out, Jerboa seems to forget the credentials of whatever account was "active", and you have to enter them in again to login. For me, the Jerboa sign-in screen has three fields, for a username, password, and instance domain.

Basically: Regardless of whether you're already logged into another account-log into a lemmynsfw.com account on Jerboa and set the instance on that account to lemmynsfw.com. Then, you end up with Jerboa knowing about multiple accounts on potentially many Fediverse instances, and you can switch in between them.