Well with GOTM40 stashed away (low-scoring Domination) I'm halfway through the shields. I'm also going to have a Green Ambulance attempt coming up soon as well, probably in the next Diety game. I don't think I'll intentionally lose, but I'll probably be able to come up with a good scoring spaceship loss or something. Here's my analysis of how easy/hard it is to get a low score with each of the victory conditions:
-20k: Very Very Easy. It can be done with a OCC and since you're concentrating just on one city with that, you never get much of a score, and most of the game you're accumulating culture, brokering tech, and keeping on everyone's good side.
-100k: Not so easy. 100k = lots of cities usually, although it can be done with 10-15 cities if you spread wonders around.
-Spaceship: Could be done OCC, but 5CC seems more likely with this. Once again most of the game you're just a tech broker trying not to be conquered, at least in a low-score attempt.
-Diplo: Would be easy but with one caveat: The 25% land requirement. This isn't to say you couldn't do OCC/5CC until the late Industrial, then conquer your share of land, but it's not as easy to "reverse milk" a Diplo game compared to 20k or SS because of the requirement to become eligible for voting.
-Domination: I had trouble getting this one, which surprised me. Best way to do it is probably stick around with few cities until the Modern Ages, then go all-out with Modern Armors.
-Conquest: Can be done OCC/5CC, just raze instead of capture. Still could be a challenge though, considering you'd need to not only conquer, but also keep other civs from filling in the razed gaps with settled cities.