No submitblock in altcoin?
Ok, took some doing but I figured it out!

It seems there a lot of which do not have submitblock in the source. Whether this is intended (mining advantages vs noobs) or just pure incompetence is not sure, but the solution requires minimal changes to the source.

I found this which should help if you're having this issue: https://github.com/earthcoinproject/earthcoin/commit/0b862e499e05386e333563656f84e99bad1b0290

Hope this helps another frustrated developer :)