Sending / replying to texts in response to Siri prompts
When sending a text with Siri, I might say, "Hey Siri, text ______ I'm running a bit late", but sometimes Siri will respond with, "What would you like me to say?" (I.e. it only understood the addressee) - at this point I can't just answer her with "I'm running a bit late", because Siri doesn't respond unless prompted with "Hey Siri" first. So I'll say, "Hey Siri, I'm running a bit late." And then the text that Siri offers to send says, "Hey Siri, I'm running a bit late."
So my real question is how do I reply to prompts from Siri without actually saying, "Hey Siri", which always get interpreted as part of the response, rather than the keyword to alert Siri...
iOS 11