Here's a comment that Jane made under the Introduction to Denting thread - hope this helps.
"Gosh, I've never done that....just thinking about it and wondering about density issues in the reed for your crammed areas. They are already quite dense with just one layer and then to double it again for 2 layers....not sure what to say other than try a sample and use a very open reed. If you try it please let us know how it goes. Sorry I couldn't give you a more solid answer. :) "