Add dynamic variables to build messages

I'm trying to dynamically build a channel message:

paragraph 1: text
paragraph 2: included only when a condition is met
paragraph 3: included only when a condition is met
paragraph 4: text

I want to send this channel message x days prior to arrival date.

YES YES YES! This is the only reason I still maintain my Hospitable account -- their conditional message ability is so robust and blows OR out of the water when it comes to being able to customize communications!