I think the answer, if you don't wish to mark up your text, is to be verbose in your intentions. A message like "Great idea." is easier to misinterpret than "G

I think the answer, if you don't wish to mark up your text, is to be verbose in your intentions. A message like "Great idea." is easier to misinterpret than "Great idea! Seriously, I never thought of it that way." Qualifiers can go a long way. They might be clumsy, but I think they're the best alternative.