After some clicking around, I think I figured out how to post to this self-hosted blog from Wordland.Social. Briefly:
- I created a new, non-admin account on my self-hosted blog and a new, corresponding WordPress.com login.
- I logged into my self-hosted blog as that non-admin account and opened the Jetpack plugin, which showed that my blog was connected to Jetpack but not my new account.
- Following the prompts, I was able to link that non-admin account to the new WordPress.com account and then use the latter to authenticate through Wordland.Social.
Straightforward? No! But a lot of that is out of this interface's hands.