So I'm capable of writing PHP and could make a version of this link work for me.
My thinking is that I would use the Trade Dangerous editor to manually key the prices if EDMC cannot send them. TradeDangerous produces an updated.prices file. I can write PHP that would parse the .prices file and send to EDDN.
My worry though is whether the EDDN subscribers would accept my 'application' from the EDDN or just chuck it away.
I'd have to learn Python to integrate this into TradeDangerous....
But if there's something out there I can use instead, that would be my preference.
At one stage I recall there was an EDDN plugin for TD which I think did what you want - ie: took an updated.prices file and sent it to EDDN. It was a long time ago though - when EDDN was just getting off the ground. You might be able to dig up the code in an old bitbucket. It wasn't a "plugin" as in the plugin folder - it was a misc script.