I was just thinking about how to get the marshmallow flavor. How bout a slurry or mixture of a small amount of maltodextrin,lactose,& vanilla to simulate the marshmallow flavor? Possibly in secondary for a short time?...Just a thought.
A guy in my homebrew club brewed a Toasted Marshmallow stout for our Extreme Beerfest a couple weeks ago. I believe he did use some toasted fluff, as well as marshmallow extract he found. I didn't get to try the beer myself (it kicked rather quickly) but by all accounts it was really good. I'll see if I can get him to share the recipe and how he used the mallow.