Searching assignee cross-repo

It would be good if ghi list -u <username> listed all that user's open issues, cross repository (without a repo, it returns the same as ghi list, regardless of which username I put, as per the documentation). I don't believe this functionality is available in the issues part of the github API, but it is available in the search part of the github API - by performing a search for assignee:<username>. I don't know if that would be easy to hook up to?