There is no such functionality, but you could try the workaround below:
- Open the main 1Password app and select one of the Logins for a site that you don't want to set as the default.
- Click 'Edit' at the bottom of the window and click the 'Display' menu that appears.
- Choose "Never Display in Browser", then click Save at the bottom of the window.
- Repeat these steps for each of the Logins you don't want to set as the default.
You'll still be able to access your work account from the app. It just won't be available in the browser you're using.