Variable replacement not working for Connection parameters

[JesseDocken]

I have a load testing script that computes a payload to send to an exchange. I wanted to be able to parameterize the connection so that I could easily point the load test at the different environments for my application, however when I try to do so (for example, setting Host to ${AMQP_HOST}), it just uses that plain string as the host rather than evaluating the hostname.