Hi Tim,
First a shameless plug for the plaster manufacturer that I work with;
http://limestrongfinish.com This is the best plaster I have ever used and the pumice makes it somewhat insulative. It is a pozzolan plaster that behaves like NHL2.
You can also make a good plaster with big box store items like type s hydrated lime and sharp sand. The three coats will have different additives like hair, pigment and possibly a pozzolan like wood ash or metastar, but this is not a difficult process.
As Jay has already stated, a plastic mesh lath is probably necessary to get a good bond to the bags. Ensure that you will have a month or so of non-freezing, decent weather before plastering so the lime can fully carbonate before foul weather hits. If it doesn't, don't worry the plaster will just need a lime wash(this is how we pep up lime plaster that is looking faded) a little sooner than usual.
If you need tips or ideas on pozzolans or colors, just post here and we'll get you going!
All Blessings,
Bill