A trick to get the paste off of plastic is hide it instead, use a close matching color shoe polish wax (kiwi is what I've used) with a toothbrush. By the time that washes away, the nufinish is either stained that color or gone too. It's even more effective if you put that on before the nufinish, then can wash it all away. Do test in an inconspicuous area, some plastic gets horribly porous/crusty from long term sun exposure and anything you put on it, will mismatch the rest. If you don't want to use a colored wax, anything else coating the plastic ahead of time will still help to keep the nufinish from soaking into the pores.
Paint thinner or mineral spirits for removal as well. On their web site.
Great idea though, will keep in mind since I don't have any other use for shoe polish.
Just did my 05 ION. Still looks like a 2 year old model.