Anyone successfully win a OCC in Conquests on Emperor+?

[RobC]

After being able to win on pretty much any difficulty level with a combination of REX-ing and artillery SODs, I thought I'd try my hand at the one-city-challenge for a change of pace. I've successfully won all the way up to Monarch, but I'm having trouble at Emperor. Has anyone successfully win a OCC in Conquests on Emperor or higher? Any suggestions or special strategies?

p.s. In 'official' OCC rules, can you accept a city that wants to defect/culture-flip to you so that you can abandon it, or does that break the 'one city' rule?