I want to add album artwork to Beat Material's last.fm page, but they have no albums listed, and I have no ability to even add them. The albums are called "And Two Photographs" and "S/T", as shown here: https://beatmaterial.bandcamp.com/
How can I add albums to this artist's last.fm page?
You can scrobble them from Bandcamp e.g. with the Last.fm web scrobbler browser extension. If they have mentioned the album names correctly there, scrobbling them should automatically create a corresponding album page on Last.fm.
Furthermore you can also check if their releases exist on MusicBrainz, and add them there if they are missing, as Last.fm imports data regularly from that site.